Here's a model (more info) that I thought was an old Buddhist thing but is actually just from Jonathan Haidt, like a number of other cool things (like Moral Foundations Theory, and a fun test about it here). Anyway, it's been a useful model for me.
You've got an elephant (your impulsive, emotional self) and a rider (the cool, calm, rational self). You can't really control the elephant, but you can learn about the elephant and steering it the right way. The elephant is much stronger, so learning to work with the elephant is way more valuable than just trying to ignore it.
I guess when people say something is hard, they mean it's an environment that's hard to drive your elephant in. Grad school is hard like that. It's full of a lot of things that aren't really problems, but will spook your elephant. (Your paper got rejected! These senior researchers think you're a fool! Your work is meaningless!) If you get better at calming down the elephant, even if you just slowly plod along forward, you'll do fine.