An addiction to stacks
Yet again, another example of self-destructive behavior that people fall into time and again. This is one that's been around as long as Nasus has, and one only further exacerbated with the advent of the Feral Flare and now the Devourer.
You know when someone declares in the chat queue "Don't lose your lane! I'm gonna rush Sated Devourer!", you're in for a bad time, cue obligatory Sans picture. When two people make this declaration, you are in for an even worse time.
Guess what happened to me the other day?
We had a Nasus and a Jungle Udyr, both of whom declared to focus on nothing but stacks for the first 20-30 minutes, both of whom who simply ignored both the enemy and the team, both of whom ended up neither stacking nor being actually useful to the rest of the team or even themselves. This isn't the first time it's happened, and I sure as hell don't expect it to be the last.
Focusing exclusively on how many stacks you have because you think you'll be invincible by the endgame doesn't work. It NEVER works against any halfway competent enemy. It deprives you of an early and mid game, and if your team can't pick up the slack in your absence, whatever YOU think you can do won't mean much, even if they do manage to hold their own. You're gambling for the illusion of invincibility, and even then you really suck at it by blinding yourself to the rest of the world around you. I've run Devourer several times in the past, and I always built Sated faster by helping the team than the enemy could dashing around the jungle. The same thing applies to Nasus or Veigar or whoever else is completely dependent on stacks. Eighteen quintillion stacks won't mean anything if your team is completely battered and smashed because you elected to ignore them for your own selfish gains. STOP IT.