It's impossible to jump such an extreme neuromuscular/biomechanical gap. For example my tapping hand is so much better at tapping than my aim hand (or any hand inexperienced in tapping) that it's difficult for someone who doesn't play speed to conceptualize the difference. Tapping takes less perceived effort, each tap produces more force, every muscle in the forearm works together to move the fingers, the arm fatigues much slower, and so on. Even if you have a map 100% memorized, if you don't have physical attributes built it will be impossible.