All-in

Small blind, 9 big blinds, A-8 suited. It folds to you. Shoving is the play - limp or min-raise and the big blind can 3-bet you off it, and folding this is far too tight. You jam, the big blind wakes up with A-K and calls, and the hand is out of your hands. No more betting from either of you - the flop, turn, and river run out with the money already in the middle.

That lack of further decisions is the whole point. Once you're all-in, nobody can bluff you off the hand and you can't bluff them off it either - the only variable left is the deck. That's how a short stack survives: jam, and the opponent never gets to outplay you after the flop. It's also how you get paid with a monster, as long as someone will call - shove too big, though, and you fold out the worse hands a smaller bet would have collected from. One more wrinkle: with three or more players and a short stack, the extra chips from the deeper stacks form a side pot the short stack can't win. That detail trips up a lot of beginners.

The common leak is treating all-in as a bigger bet instead of a different kind of decision. Players jam for value when a smaller bet would get called by worse - winning less, not more, because the shove scares those hands off. Or they bluff-jam without asking whether their stack is big enough to make folding the right move for the opponent. Same action either way. The chip count changes what it means.