Most here are also perfectionist, me included. That's why there's so much frustration.
Relax while your doing it, the more you concentrate the more you're focusing on what you're doing the more frustrated you'll get.
Get paint in the brush and paint something, anything. Try to focus on the paint hitting the paper rather than what your trigger finger is doing. Eventually the brain takes control and before you know it you've built that elusive muscle memory in your finger.
It will happen I promise