I might redefine that as 'you can stay irrational longer than you can stay solvent'. Blaming the market for irrationality is in practice used as an excuse for being wrong. I am actually correct but the market isn't as right as me!
this is when people get butt hurt after missing the 10 year long rally and numerous chances to BTFD... so they have to suck on a pacifier and say to themselves - well, it will crash soon. instead of doing the above, why not sit down and think it thru... it's not too late... the DOW next target is 40000.... get in, get rich... put up or shut up.
What is the market fair value right now? nobody knows. so technically the market is wrong all tge time. Then there is the fact that the smart dumb money ratio is about 2:8. so with this much dumb money in the game. its even more impossible to get to the fair value.