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The Role of Luck and Skill in Investing

by Charles Rotblut, CFA and Michael Mauboussin

Michael Mauboussin is head of Global Financial Strategies at Credit Suisse and the author of several books, including “The Success Equation: Untangling Skill and Luck in Business, Sports, and Investing (Harvard Business Review Press, 2012). He and I spoke about the role skill and luck play in investing.

—Charles Rotblut

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About the author

Charles Rotblut is a vice president at AAII and editor of the AAII Journal. Follow him on Twitter at twitter.com/CharlesRAAII.
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Michael Mauboussin is head of Global Financial Strategies at Credit Suisse and the author of several books, including “The Success Equation: Untangling Skill and Luck in Business, Sports, and Investing” (Harvard Business Review Press, 2012).
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Charles Rotblut (CR): A big theme in your recent book is the distinction between skill and luck. Could you explain what the difference between the two is?

Michael Mauboussin (MM): One of the ways I like to think about this is as a continuum of activities from pure luck and no skill on one end to pure skill and no luck on the other end [Figure 1]. Obviously, most things reside somewhere between the extremes, and where an activity sits can be very important. But before we get going, it is important to define the terms.

I’m going to define skill right out of the dictionary: The ability to apply one’s knowledge readily in execution or performance. You know how to do something, and when you’re asked to do it, you can do it effectively.

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Luck is much more difficult to define. It actually spills into moral philosophy pretty quickly. I’m going to say that luck exists when three conditions are in place. Number one, it operates on an individual or an organizational basis, such as you or your team or company. Second, it could be good or bad. By that, I don’t mean to suggest that it is symmetrical, as in it could be equally good or bad. But rather there is a plus sign or a minus sign. The third thing is that it is reasonable to expect that a different outcome could have occurred. If those three things apply, then you’re in a situation where luck exists.

Not surprisingly, when you look out into the world, whether it’s business, investing or your favorite sports team, both skill and luck are contributing. The real question is, in what proportion?

CR: Do you think investors confuse the two when looking at their own performance, in that they think they are skillful when they have actually gotten lucky?

MM: There is actually a very interesting test to determine if there is any skill in an activity, and that is to ask if you can lose on purpose. If you can lose on purpose, then there is some sort of skill. Investing is very interesting because it is difficult to build a portfolio that does a lot better than the benchmark. But it is also actually very hard, given the parameters, to build a portfolio that does a lot worse than the benchmark. What that tells you is that investing is pretty far over to the luck side of the continuum. That is the first important thing.

The second thing is that luck is a very difficult thing for us to deal with psychologically. The main reason has to do with a part of your brain in the left hemisphere. If you give it any effect, it will immediately and effortlessly come up with a cause. That part of your brain knows nothing about luck. It only knows about causality. So it attaches skill to positive outcomes and it attaches lack of skill or maybe bad luck to poor or negative outcomes. So there is this kind of disconnect between what happens in the real world and how our mind interprets those events. And to your question, we tend to associate good outcomes with good skill alone and that’s often simply not the case. And bad outcomes are not necessarily associated with bad skill either. It’s a very tricky relationship to understand clearly.

CR: If someone is following a set process of picking stocks or bonds and it doesn’t do well, is this a case where the investor should look at how the strategy has performed in the past and if it has worked well, just attribute the poor performance to luck turning against them?

MM: For sure. Part of what I talk about in the latter part of the book is how to improve one’s skill. What I argue is that when you’re on the skill side of the continuum, your output and your skill are very closely related to one another. If I want to know if you’re a good violin player or a good tennis player, I can listen to you or watch you play and I can tell quite quickly. When you move over to the luck side, it becomes process-oriented and probabilistic. For example, there is a standard strategy for blackjack. You may play your cards properly and lose the hand, which is just bad luck, or you may play your cards foolishly and win the hand. So the connection between the quality of your skill and the outcome is broken. There, you really have to focus on process.

How do I know if my process is any good? Number one, has it worked in the past and is it economically sound? Number two, I think of good processes as having three essential elements. Element one is analytical: having an ability to find situations in which you believe something the world doesn’t believe and in which you have a good foundation for such a belief. The second is behavioral: we are all subject to behavioral mistakes and cognitive biases. Are you aware of those things and are you taking steps to manage or mitigate them? The third, which is less true for individuals and truer for organizations, is what I call institutional. This element relates to the constraints in your personal or professional life that don’t allow you to do the best thing possible in terms of your process. If you have a good analytical process, are aware of behavioral issues and organizational issues are not a problem, then you typically can develop a pretty effective process. If you’ve done that and you get a bad outcome in the short term, you pick yourself up, dust yourself off and you go back at it the next day because over time the process will lead to success.

Charles Rotblut, CFA is a vice president at AAII and editor of the AAII Journal. Follow him on Twitter at twitter.com/CharlesRAAII.
Michael Mauboussin is head of Global Financial Strategies at Credit Suisse and the author of several books, including “The Success Equation: Untangling Skill and Luck in Business, Sports, and Investing” (Harvard Business Review Press, 2012).


Discussion

Shane Milburn from TN posted 11 months ago:

Really good interview. I wasn't aware of "active share" stats. I'll have to look into that for funds.

re: "In fact, people tend to buy what has done well and sell what has done poorly."

I'm not sure I understand where this is coming from. I only mention this because I think tendency is opposite - to sell winners and hang on to losers. To the contrary, I've found the advice of selling winners and buying losers to _not_ be a good strategy for me.


Peter Asprey from CA posted 11 months ago:

One of the better recent interviews for my purposes. Thank you.

I've struggled with how much of the returns in my system are "Luck" and how much are "Skill." Only the most egocentric would assign a lot of skill, and those folks are riding for a fall.

That said, I chair a group system, called TtP-S which deals with very high quality dividend paying stocks, in a blended investing and trading model. It follows a set of tight rules. I found myself assessing the relevance of each response by Mr Moubaussin's to our own investing system, and lots of spotlights (and a few alarm bells) went on. AND, we cover a bunch of his principles pretty well too.

I've pointed my group to this article and offered and investment book as a prize for the best posted analysis relating this article to what we do.

Thanks again for an excellent article! Luck? Skill? Mean Reversion? Good stuff.

Pete Asprey
9/2013


James Hargreaves from GA posted 11 months ago:

MM is fundamentally wrong in his "outlook" as to what luck is (or is not).

MM confuses luck and chance.

MM also clearly doesn't understand philosophy of science and the scientific method.

CR makes a very important point at the start of this article/interview with his first question. It ALWAYS makes sense that one define their terms before one tries to have an intelligent argument using those terms.

MM also properly points out that the "difference" between luck and skill very quickly gets into philosophical issues.

Unfortunately, MM quickly seems to dismiss many of those philosophical issues (or at least does not delve into them).

For example, in statistical decision theory and game theory, one has (or develops) a state of nature (framework) within which the decision making process is conducted. Just because one has a "model" of reality that one assumes is correct DOESN'T MEAN that that model is either complete or correct.

In my philosophy of life (pyramid of principles) for life and stock trading, at the top of the "pyramid" (the capstone principle) is what I euphemistically call the "Shit Happens" principle.

"Shit Happens" summarizes three basic facts. First, whatever you are sure of at any given point in time is subject to change without notice. Second, at any given point in time, we KNOW there is a bunch of "stuff" we DON'T KNOW that we need to know to eliminate all risk in our decision making process. Finally and third, there are a bunch of factors that we aren't even aware of (in life and trading)- let alone do we know what those facts are.

Thus, in life and trading, ANYBODY who proceeds without fear and trepidation and a healthy does of humility and search for the "Truth" is bound to have GREATER FAILURE in their pursuits than someone who is eternally vigilant and always is seeking a better understanding of their situation.

Seek, know, and accept the Truth, and the Truth will set you free (as much as possible).

Knowledge is power.

By the way, the "Shit Happens" title is made meaningful to me by my experience with dairy farming.

When I was in my teens, I worked, in the summers, on my grandfather's dairy farm. He had about 200 cows.

At about 0500, I would have to head out across the farm (from our residence (on the eastern side of the farm) to the milk barn (on the western side of the farm). I had to walk through a 50 acre field where the 200 cows were put out to graze during the day.

I crossed that 50 acre field in the dark. Each step carried with it the real possibility that I would step in a "cow pie".

Some "cow pies" had had time to fully dry (and could be stepped on without consequence). Some "cow pies" had only dried on the outside and still had a mushy middle which one could "discover" by stepping on the apparently "safe" cow pie and sinking in. Finally, some of the "cow pies" were still in the newly formed stage. They were just one big pile of mush. The name mush was appropriate because stepping on them was what it sounded like.

Such is life (and trading). A field filled with "cow pies" which one must cross in the dark. Even if one traveled that "road" every day (in the dark and light), it was subject to constant change. Mentally logging the location of particular "cow pies" (especially the mushy ones) had it's merits. However, no matter how careful or thoughtful one was, you better count on stepping it it on occasion.

By the way, sometimes they would leave the bull out in the field when they brought in the "herd" to be milked. The bull in that pasture was what in finance might be called a "black swan" event.



James Hargreaves from GA posted 11 months ago:

MM is fundamentally wrong in his "outlook" as to what luck is (or is not).

MM confuses luck and chance.

MM also clearly doesn't understand philosophy of science and the scientific method.

CR makes a very important point at the start of this article/interview with his first question. It ALWAYS makes sense that one define their terms before one tries to have an intelligent argument using those terms.

MM also properly points out that the "difference" between luck and skill very quickly gets into philosophical issues.

Unfortunately, MM quickly seems to dismiss many of those philosophical issues (or at least does not delve into them).

For example, in statistical decision theory and game theory, one has (or develops) a state of nature (framework) within which the decision making process is conducted. Just because one has a "model" of reality that one assumes is correct DOESN'T MEAN that that model is either complete or correct.

In my philosophy of life (pyramid of principles) for life and stock trading, at the top of the "pyramid" (the capstone principle) is what I euphemistically call the "Shit Happens" principle.

"Shit Happens" summarizes three basic facts. First, whatever you are sure of at any given point in time is subject to change without notice. Second, at any given point in time, we KNOW there is a bunch of "stuff" we DON'T KNOW that we need to know to eliminate all risk in our decision making process. Finally and third, there are a bunch of factors that we aren't even aware of (in life and trading)- let alone do we know what those facts are.

Thus, in life and trading, ANYBODY who proceeds without fear and trepidation and a healthy does of humility and search for the "Truth" is bound to have GREATER FAILURE in their pursuits than someone who is eternally vigilant and always is seeking a better understanding of their situation.

Seek, know, and accept the Truth, and the Truth will set you free (as much as possible).

Knowledge is power.

By the way, the "Shit Happens" title is made meaningful to me by my experience with dairy farming.

When I was in my teens, I worked, in the summers, on my grandfather's dairy farm. He had about 200 cows.

At about 0500, I would have to head out across the farm (from our residence (on the eastern side of the farm) to the milk barn (on the western side of the farm). I had to walk through a 50 acre field where the 200 cows were put out to graze during the day.

I crossed that 50 acre field in the dark. Each step carried with it the real possibility that I would step in a "cow pie".

Some "cow pies" had had time to fully dry (and could be stepped on without consequence). Some "cow pies" had only dried on the outside and still had a mushy middle which one could "discover" by stepping on the apparently "safe" cow pie and sinking in. Finally, some of the "cow pies" were still in the newly formed stage. They were just one big pile of mush. The name mush was appropriate because stepping on them was what it sounded like.

Such is life (and trading). A field filled with "cow pies" which one must cross in the dark. Even if one traveled that "road" every day (in the dark and light), it was subject to constant change. Mentally logging the location of particular "cow pies" (especially the mushy ones) had it's merits. However, no matter how careful or thoughtful one was, you better count on stepping it it on occasion.

By the way, sometimes they would leave the bull out in the field when they brought in the "herd" to be milked. The bull in that pasture was what in finance might be called a "black swan" event.



Christian Hansen from AZ posted 10 months ago:

Terrific discussion and insightful comments. What I always wonder about is, what is the metric to determine the chance/skill ratio? We are guided to use indices, typically the SP500; yet these are themselves selected, non-random samples for various reasons. It has always seemed to me that the true metric is a random sample of say, all U.S. equities (or a ditto limited to your investing universe). For good statistical accuracy, it does not have to be a big sample, maybe 50; but there are issues in how often to do the sampling, factoring in typical transaction costs, and so on. So does this index already exist?
Second, more philosophical point: All investment analysis tends to have myopia - it assumes that the world won't get hit by an asteroid tomorrow. Or, that there will be a world war, or a plague, or you will contract a terminal disease, or get run over by a bus. So there has to be, on top of all investment analysis, a personal trade-off between current and increasingly delayed (future) gratification, like the promise of retirement. Only you have the data to make an educated guess for what makes sense for you. Thus investment analysis is only one facet; other important factors are education, profession, health, geographical location, and spouse/family "investments." The biggest investment risk of all is dying with money in the bank! (That keeps me awake at night.)


Bruce Ballengee from Texas posted 10 months ago:

Perhaps our authors might pontificate on this idea: Given the large random element of luck don't the tried and true principles mentioned such as maintain a diversified portfolio consistent with a well-thought out risk profile(which means selling high and buying low at times) combined with avoiding all unnecessary expense (indexing, low fees, buy and hold, etc.) and dollar cost averaging in the case of retirement accounts in accumulation or distribution mode, all work precisely because of the large element of luck involved. These are the tools one uses to maximin randomness' harmful and beneficial effecfs. Maybe there is some causality,just very, very hard to ferret out all the positive and negative feedback loops that net to "randomness". J


Robert Kraft from NE posted 10 months ago:

Very nice article, thank you.


Fernando Robles from FL posted 10 months ago:

Luck: Being at the right place, at the right time for both, good or bad. What a life!


Emmanuel Daugeras from France posted 10 months ago:

Very interesting article.

Investing by the ratios in a systematic way is an attempt to have luck on one's side: long term statistical studies (O'Shaughnessy) show that long term returns are almost determined by the valuation metrics that you are willing to pay (the lowest ratio you pay for while investing, the greater the long term return). It is very hard to predict the particular outcome for each stock, but the law of large numbers provides more good surprises than bad for cheaper stocks...


Charles Foxx from NM posted 10 months ago:

I enjoyed this thought-provoking article. But I disagree with the last statement regarding having success on one's first investment is a detriment to learning which things are important for the possibility of a good outcome.

I was part of a team developing a new chemical process. Our first experiment was a partial, if not perfect, success, then we had six failures in a row. It is true that you can learn more from your failures than your successes. But without that first success, we might have given up on believing that it could be done. We just had to figure out what parameter(s) was right in the first experiment that wasn't right in the next six attempts.

Similarly in the world of investing, if one has to start with six losses in a row, it might make you think a lot about what went wrong or it just might make you place all your investable money in a savings account and never invest again. Whether it is skill or luck, a little encouraqement is not a bad thing. There will be plenty of learning opportunities for skill development, if one examines the losing investments against the insights of other investors, analyzes what appears to have gone awry and searches out what actions appear to have contributed to success. Yes, luck confuses the process, but experience can sharpen our understanding of what increses the probability of success.


David Lash from CO posted 8 months ago:

In the print article the third line indicates that the author is innocent of basic probability. My father taught me some 60 years ago the first law of probability, " Chance has neither memory nor chance!". The notion that past experience changes probabilities for the future is equivalent to believing that last weeks lottery loss increases next weeks likelihood of a win. Nonsense
dgl


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