Yeah, I can't say lemmas are (generally, or even often) simple and obvious. To me, they often seem arbitrary: what do you mean before we prove this grand theorem we have to prove these completely unrelated lemmas? Okay, proved the lemmas. Now the proof of the theorem has "according to such and such lemmas..." sprinkled around, but I've already forgotten what the lemmas were and why they're applicable. I also can't name any lemmas that changed how I think.