When I am struggling with something, I sometimes think 'Damn, this is hard. I wonder if I am stupid,' and then I remember that I have a counterfeit degree in astrophysics from Cal Tech; I might be stupid, but I can still fool others.

When I am struggling with something, I sometimes think "Damn, this is hard. I wonder if I am stupid". And then I remember I have a PhD in solid-state theoretical physics, and I think "Man, I used to be smart -- how did I manage to become so stupid since then?"

When I am struggling with something, I just give up.

"If something's hard to do then it's not worth doing." - H. Simpson

"And if something is not hard to do, why try at all." - Paras Chopra