I've learned, having been on a lot of sets, the good news is that by definition you are surrounded by experts. They get fired if they're not - unlike in the theatre!
In theater, you've got to be aware of your whole body because it involves stamina. It involves two-and-a-half hours and a sustained release of energy, maybe for six months.
I'm very aware that when one is acting in the theater, you do become kind of animal about it. And you're reliant on instincts rather than tact a lot of the time.