Often we judge the success of an activity by its outcome. We run a sprint, we know at the end who has won. We write an exam, results in few hours/weeks tell us how we did. When outcome is immediate, cause and effect relationship is easy to understand.
However, this outcome based evaluation can mislead if the outcome occurs, not immediately, but over long periods of time. More so, if immediate outcomes are different from long term outcomes. Consider healthy eating. Giving away junk food for healthier alternatives look painful today but is beneficial in longer run. Or consider working out. Going to the gym looks a chore in near term but immensely beneficial eventually. Conversely, smoking or gambling may feel great in the near term but are harmful over longer term.
For such activities with longer term outcomes, a judgement based solely on immediate outcomes – healthy eating or workouts are undesirable, smoking or gambling are desirable – will be wrong.
Investing is more like the latter set of activities. There is an element of luck in the near term which can lead to false positives – great returns despite buying wrong things; or false negatives – poor near term returns despite correct process.
If the immediate outcome of an activity is poor, how do we know for sure that we need to stop or continue that activity? We need to look at historical evidence of longer term effects. And we need to ask whether it makes sense in longer term.