I don't think the saying is really tied to any particular prediction. Surely there are times when you felt the market was behaving irrationally? The saying is a

I don't think the saying is really tied to any particular prediction. Surely there are times when you felt the market was behaving irrationally? The saying is a warning about taking action in such times. Because even if you are ultimately right, you may still end up a big loser. I.e. the whole point of the saying is that it's not just about whether there's actually a bubble or not. You're also taking risk with how high it will go/how long it will last before popping. So a consumer investor may just buy stocks they think will eventually go up, and won't encounter major problems with that, but shorting just because they think something will eventually go down is a whole different beast.