I don’t have a ton of Tonys or anything (just six) but if you find a role/ensemble cast that you enjoy working with, it’s hardly work. Plus, it’s a labor of love. Once you can read your lines like the back of your hand is actually where the fun really starts. It’s been said already, but changing inflections, adding words and overall having fun with a role really makes a difference!
Any stage show I did and my job of tour guiding in college all boiled down to the same thing: memorizing and reciting the same lines over and over, but doing it in such a way that it was new every time.
As for keeping the energy level up, I just told myself “This may be the thousandth time I’m doing this action, but this is probably the first time they’re seeing me, so act like it.”
While you’re feeling sorry for stage actors, give a thought to the musicians whose job it was to play into microphones to record songs back in the day before electric recordings. Think Edison cylindrical records. Everything was mechanical, and the most they could record at once was 12 or 13 copies, and depending on the number of copies wanted they could finding themselves playing the same song literally hundreds of times. I understand that this would sometimes come close to rendering them bonkers.
I love acting. I love stage acting. I was asked to help out a “learn to act” group by being in the class as a bit of a “ringer” and the teacher said that “You can tell she REALLY loves it and that should come across”. The energy from the audience, their reactions, those are new each and every night, and that just feeds you.