Variance is a scary thing, yes. You could simply end up being a bottom 5% run (not unlikely - 20 in 1 chance) and then you're ****ed almost no matter how much you play. Unless you get
really really good.
You could also get the top run and print, who knows
But yea, variance calcs are hella scary to think about
This is also a good reason to chase games where you are more than a 3bb winner. Going just a few bb's above that largely negates this whole thing. 8bb+ winrates look hella linear at larger sample sizes. Smooth sailing (in comparison to the low winrates).