This sort of reminds me of the old pottery story, where they had one group making which was graded on how many pots they made and another one which was only graded on their best pot. Of course the group which was graded on quantity made better pots in the end.
I really think that by iterating really quickly you will become good faster than if you try to make the perfect thing right away. So don't be paralyzed by trying to achieve perfection; go out and create, and then create some more.
You certainly do have to modify that advice to avoid serious injury, but from my limited boxing experience I'll say that nothing teaches you to keep your hands up like getting smacked around a few times.
I really think that by iterating really quickly you will become good faster than if you try to make the perfect thing right away. So don't be paralyzed by trying to achieve perfection; go out and create, and then create some more.