More recently (last 20 years) Economics has taken a new turn towards incorporating Prospect Theory. I won’t bore you with the nitty gritty details of this subject, but there is one finding extremely relevant to trading. In the context of the trade example, if you are up 10% and the market has a high probability of rallying to a gain of 20%, most people would take their profits and cash out. Why, because the thought of making some money, is more important to traders as the notion of losing some of the gains by a trend reversal? Incorrect. Consider the opposite scenario: if you are down 10% on your position, it is proven that a large majority of people, instead of cutting their losses, all of a sudden become “investors instead of traders” and sit back hoping for the market to rally back. Cries of “HODL”, (“Hold on for dear life”) are commonly chanted amongst traders, when this situation occurs. Wouldn’t logic dictate that if people value the thought of making less money rather than losing money and hence close out early on winning trades, dictate that presented the exact opposite scenario, people would cut their losses and cash out?
It turns out, according to Prospect Theory, that people overvalue events which have a low probability, and undervalue events with high probability. In our example, if down 10% on a trade, if there is a 10% chance of a rebound to breakeven, you might in your head consider that to be a 40% chance, hence making a losing choice of “HODL”. Similarly, if there is a 60% chance of making noticeably more money on a winning trade, you might in your head consider that there is only a 30% chance of more gains, and cash out.