Say for example you're 3 handed in the end-game. You have an M around 10, there's a shorty with an M around 3, and a big stack with an M around 30. Obviously you have to avoid the big stack, and you can take gambles with the shorty, but you can't really press the shorty because if he doubles up through you you're even. What you want to do is just sit back and wait for the big stack to knock out the shorty so you can move up in the money and play heads up.
The problem occurs when the big stack is awful and keeps failing to knock out the shorty, either by folding to his pushes, not pushing enough at his BB, or just playing bad and giving him chips. If the big stack really plays awful against the shorty it can be a huge impact on your EV in the tournament, which sucks bad.
I get really frustrated in all multi-player games when you have to rely on other people making sensible moves. It's like when you're playing Risk and player B can easily take a province to keep player C from getting all of Russia on his turn, and he doesn't, it just fucks you over and you aren't even involved. Ghey.