Everyone always thinks they're right and the market is irrational. But taking the outside view, at least some of the people who think the market is irrational are actually just wrong and the market is right. And those are the people who will observe the market staying apparently-irrational the longest!
Yeah, markets can stay irrational longer than you can stay solvent. But also you can stay wrong longer than you can stay solvent. And it's much easier to be personally wrong about something than for the market in aggregate to be wrong about something. So you have to expect that, most of the time, if you disagree with the market, you are in fact wrong.
Is another way of saying "I am not putting my money where my mouth is".