Ace high flush but possible beaten by one card straight flush.Maybe you are close to the money or a big pay jump. You don't really want to take risk right now but you look down at a big hand. Some players move all in which would put you all in. You go back and forth whether to fold or go all in but you make the fold. What's the biggest hand you've ever folded pre flop? What was the reason for the fold? I've folded KK once and don't think I ever will again. I was on the money bubble and regretted it. I would have won against 2 all ins.
Folded even AA if it's the beginning of _really_ cool tournament and some fishes mindlessly go all-in.