In my experience "deciding what you’re going to throw away" is also a very sound first step in portfolio management. Rummaging through the discard bin from time to time is pretty good as well.
I've found another problem with simple numbers/metrics that reflect some slice of reality is that the ones that are the most accurate at tracking that slice are too slow to be useful in making decisions when the time comes.
In my experience "deciding what you’re going to throw away" is also a very sound first step in portfolio management. Rummaging through the discard bin from time to time is pretty good as well.
Closely related is the Goodhart's Law problem. Once you pick a single number as your target, it ceases to measure what you thought it was measuring
I've found another problem with simple numbers/metrics that reflect some slice of reality is that the ones that are the most accurate at tracking that slice are too slow to be useful in making decisions when the time comes.