The Little Book of Behavioral Investing: How not to be your own worst enemy

Chapter Two

Who’s Afraid of the Big Bad Market?

Re-Investing When Terrified

 

 

 

 

 

 

LET’S PLAY A SIMPLE GAME. At the start of the game you are given $20 and told the following: The game will last 20 rounds. At the start of each round you will be asked if you would like to invest. If you say yes, the cost will be $1. A fair coin will then be flipped. If it comes up heads you will receive $2.50. If it comes up tails, you will lose your $1.

Now there are two things we know about this game. First—and perhaps most obvious—it is in your best interest to invest in all rounds due to the asymmetric nature of the payoff. That is to say, you stand to make more than you lose in each round; the expected value per round is $1.25, giving a total expected value to the game of $25. In fact, there is only a 13 percent chance that you’d end up with total earnings of less than $20, which is what you’d have if you chose not to invest at all and just kept the initial endowment. The second thing we know is that the outcome in a prior round shouldn’t impact your decision to invest in the next round—after all, the coin has no memory.

However, when experimenters studied this game they found some very unusual behavior.⁸ They asked three different groups to play the game. The first group was very unusual; they had a very specific form of brain damage—these individuals couldn’t feel fear. The second group of players were people like you and me—ostensibly without any evidence of brain damage. The third group ...