Surviving huge fields. How?

I have been playing poker for a little less than two years. I play 1 to 5 table tournaments ($1-$10)at pokerstars. I can win with some consistency. However, i don't understand how people survive the larger fields of 1000 people and up. As the tournament starts (everyone with 1500 chips) I try to find a decent hand to play but in only 20 minutes there are already players with as much as 20000 chips. Thereafter I end up being short stacked fighting for my survival while their stacks continue growing.
Perhaps this is a silly question but is there something I am missing about tournament games online? Someone always wins those big tourneys but were they just incredibly lucky or do they know something I never heard of.
Any input would be appreciated.
Thanx in advance!