I just have to post this, from Harrington's book :

What’s the situation in the tournament? If it’s early in the tournament, and both you and the reraiser have plenty of chips in relation to the blinds and antes, you want to play more conservatively. You should be much less inclined to get involved in a situation that could knock you out of the tournament quickly. As your stack shrinks and the blinds pressure you more, your willingness to make a big move increases.