"perfect practice makes perfect" - wow this comes as a revelation to me. Never realized how important it is to do it right - something very obvious but struck me by surprise when you put it this way.
It is more complex than that though. Imperfect practice is just fine so long as you recognize in practice what you are doing wrong and try to correct it. I often practice a musical piece wrong, I try again and again, each time trying to correct something, but somehow one correction breaks something else. The next day I come back and I'm much better because even though none of my practices was perfect. Repeat a few times [hundreds in some cases] and I can play perfectly.