If you’ve been playing some large-field MTTs then you may have found that the latter stages of the game are tough.
This article from PokerSite.org is a very basic guide to forming an approach to this stage of a MTT.
If you find you are frequently making the money in large-field MTTs and then see your stack being slowly ground down while you wait for a premium hand, then your late stage MTT strategy is flawed.
3-bet shoving your whole 18bb stack with A4s against player who opens frequently may feel horrible, but look at it this way: unless you start making moves like this more regularly, you’ll just keep sagging and drooping out of tournaments without the big money anyway.
If it’s do or die, it’s better to do.