> Whenever there's a commonly-relied-upon signal, there's someone trying to mimic it, thus lowering the value of the signal.

Goodhart's law: When a measure becomes a target it ceases to be a reliable measure.

The other day someone was lamenting the disappearance of the downvote indicator from YouTube videos, which makes it impossible to use an up/down ratio as heuristic for quality. Sometimes the measure is so good that it's the custodians of the community themselves that become bad actors.