Sep 202012

Stocks that do particularly well leave investors in awe, wondering whether they could have predicted the appreciation. The Efficient Market Theory says that is impossible. Only news can move stocks prices. Hence, those stocks must have appreciated for reasons that were unknowable in advance. Nothing that was known before the price move could have helped to predict it.

This is true in many cases. But it is not always and necessarily true. The EMT is wrong: spotting bargains in advance is a difficult but not impossible task. To its credit, however, while it gives the wrong answer, the EMT does ask the right question: if you are predicting that a stock will appreciate, what do you know that the market doesn’t?

Answers to this question can be pretty weak. As ex US Secretary of Defense Donald Rumsfeld famously said:

There are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns – the ones we don’t know we don’t know.

Known knowns are useless at predicting price moves. In this respect the EMT is right: what everybody already knows must be reflected in current price levels. Thinking otherwise is what Howard Marks calls First-level thinking – definitely not a good investment method.

Known unknowns are what most investors spend their time thinking about. Taking the current price as given, investors use all sorts of information trying to predict what is currently unknown but will likely cause a price change in the future, once it becomes known. Here the EMT is wrong: the fact that information is available does not mean that everybody has the same expectations. People interpret information in different ways and can draw different conclusions from the same evidence. However, while predicting the future can lead to investment success, it is also fraught with risks, as the future is highly uncertain, often more than we are lead to believe.

Unknown unknowns are what Nassim Taleb goes on and on about. The unpredictable can happen. But, apart from writing books, there is not much one can do about it, other than trying to figure out as much as possible, being aware of the risks and avoid overconfidence.

But there is a fourth element in Rumsfeld’s matrix:

Unknown knowns are things that we are not aware we know. It is available information that we fail to take into account because a blind spot prevents us from seeing it. The Prior Indifference Fallacy renders the Base Rate an unknown known. Prior indifference explains the power of experts – be it a confident coach saying that your child is a champion or Mr Market saying that the price is right.

Investors who take the current price as given and focus entirely on predicting the future are likely to miss the best and safest opportunities for spotting bargains. Rather than trying to predict where the price will go tomorrow, investors are better off thinking where it should be today, allowing for an ample Margin of Safety.

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  2 Responses to “Unknown knowns”

  1. This holiday I read “thinking fast and slow” by Daniel Kahneman (isbn 978-0-141-03357-0 ) which was really very good and takes a more psychological/behavioural approach to some of these issues.Even faced with the truth/facts and/or quantifiable odds, we still make irrational decisions, …are still influenced by mass behaviour even if the rational decision is to do something else. The suggestion is that “knowns/unknowns etc” are not that relevant really. If you haven’t read it I strongly suggest you do.
    Thought for the day – Imagine there is an event in which you may win a huge prize, but the odds are roughly 14 times more likely that you will get killed going to the event, before you even get there to enter. Would you take the risk, or stay at home, safe ?



  2. Great read, Richard. Kahneman is in the background in many of my posts. In fact the very first post in the blog is about his book. At the bottom of this post you can find a link to an early Tversky-Kahneman paper on base rate neglect, which is the unknown known which I referred to here.

    About your question, it depends on the odds. Anybody who goes to the shop around the corner to play the national lottery runs a much higher chance of a fatal accident than of a huge win.

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