Some people work that way - theory into practice:

"But if you don't understand it how can you do it well."

But we don't all. For a lot of people it's the other way round, the theory comes out of the practice:

"You can only begin to understand it when you have learnt how to do it well"

Often enough each sort of person thinks the other way of thinking can't be real, and people must be putting it on. But it really is like that, and there's no point in arguing which is better. Like left-handed and right-handed. Or left-brained and right brained.