One key reason past performance cannot be used to predict future returns is because market expectations tend to price in expected future returns. Also, nothing competitive is expected to generate economic profit forever— in the long run things even out. In the long run, firms and stock pickers usually end up with normal profit.
But that doesn’t mean you can’t get some useful ideas about future performance from a person’s past results compared to other humans. There is no such effect in play here.
Otherwise, time for me to go beat Steph Curry in a shooting contest.
Of course there’s other reasons past performance is imperfect as a predictor. Fundamentals can change, or the past performance could have been luck. Maybe Steph’s luck will run out, or maybe this is the day he will get much worse at basketball, and I will easily win.
But that doesn’t mean you can’t get some useful ideas about future performance from a person’s past results compared to other humans. There is no such effect in play here.
Otherwise, time for me to go beat Steph Curry in a shooting contest.
Of course there’s other reasons past performance is imperfect as a predictor. Fundamentals can change, or the past performance could have been luck. Maybe Steph’s luck will run out, or maybe this is the day he will get much worse at basketball, and I will easily win.