how can big PPS pools stay alive...But I'm new to this world, and I have some naivety to wear off.
They can't, not indefinitely anyway. All PPS pools either go bankrupt or change their payout method to stay viable. It has happened over and over. The same will eventually happen to f2pool too.
It's a reason why PPS pools charge a fee to miners - to try and help offset the statistical variance the pool is subject to. I'm pretty sure I read a post on here not too long ago that gave the odds... and those odds are pretty dismal looking if you're a pool owner. Something like you needed to have at least 1500
BTC in a reserve to have a tiny chance of avoiding going broke if you're a PPS pool charging 5% fees.
Ahh... here's that post:
https://bitcointalk.org/index.php?topic=854368.msg11149806#msg11149806The referenced paper by Meni in that post is a great read.