ICM
Independent Chip Model: in tournaments chips aren’t cash, so survival has value and you fold spots you’d call for money.
Five players left, top four get paid. The short stack, 12bb, shoves from the cutoff. It folds around to you in the big blind with A-9 offsuit and 25bb, second shortest at the table. On chips alone it's an easy call: a 12bb shove is wide, your equity is fine, and in a cash game you snap it off. But one player busts before the money, and if that's you, you leave the min-cash behind — a payout jump worth far more than this pot. So you fold. The big stack in the small blind, with nothing to gain from the variance, folded ahead of you for the same reason.
That's the edge ICM gives you: a call that prints in chips can lose money in dollars, and it cuts both ways. Big stacks lean on it, shoving over the medium stacks near the bubble because those stacks have the most to lose by busting before the money. The pressure forces folds you'd never get in a cash game.
The common mistake is playing the bubble like chip-EV poker — snap-calling a good hand because "it's ahead," without checking who else is left and how short they are. ICM depends on the whole table, not your stack alone. Your equity in the prize pool shifts with every stack still in, and the shortest one changes what everyone else should be doing.