At its very best, an erection is a positive thing, a shining moment. To do that, you have to find a tremendous disassociation between your heart and your dick. A guy's only as good as his last two or three movies. He's not allowed to have a slump, he's not allowed to have a normal human day. I call it spelunking.
Some guys have to spelunk some very icky places.
Some guys, by the time they get to you, they're so jaded that they can't look you in the eye. You'll notice some always have sex the same. No matter what the scene, no matter what character they're supposed to be playing. This is how it works for them, they can't deviate from this. They can't examine themselves.