There's another element in there. The one about relative skill. Let's say that you're a much better player than the other person, and that you would win 90% of the time heads up (one on one, which we are going to assume at this point for simplicity). If this were the case, you would need to have a greater than 90% chance to win the hand all in for it to be a correct move.<p>This is also easy to understand if you, a novice, are heads up against one of the pros. It's a much better move for you to go all in on any decent hand and just try to get lucky to win, since if you try to play their game, you're going to lose.