As others have mentioned already, you need to learn to play with different stack sizes all the way down to less than 10BB, where you are typically going to be in push or fold mode. You also need to understand ICM at least at a very basic level. ICM exist in tournaments, that pay more than one player, because even you win all the chips, you dont win all the money. And because of this losing chips is always more bad, than winning chips is good, especially if you lose a significant portion of your stack.