Stupidity has always been terrifyingly powerful.

That's literally the meaning of the statement "the market can stay irrational longer than you can stay solvent".

Irrational means stupid.

Stupid can win for a very long time, and in the end the "loss" is born mostly by bag-holders.

Because it's not a single data point, intelligence is a wide surface area where you can be smart in some areas and stupid in others. Furthermore whether you are being intelligent is relative to ideals and goals, and not everyone has the same ones.

you're likely working under an assumption of meritocracy/overvaluing of kinds of intelligence