You will lose if luck is against you, even if you make every correct decision. But rather than "luck," you must account for variance and probability. If the big stack shoves preflop from the button, and you are holding AA in the blind, you call knowing you will lose the hand once every five times.
Even omitting luck, there is no perfect way to play. Should you risk your stack (and tournament life) with a 60% chance to double up? Or should you build your stack by attempting some steals and wait for a better chance? Sometimes sticking around is the best play, and sometimes it is better to roll the dice.
The goal is to play your best game and forget about the variance. You will lose at times no matter what you do. But just as often, the luck will be on your side.