The cliché goes: Amateurs practice until they get it right; professional practice until they can’t get it wrong.
This is probably quite a good generalisation. What I find interesting is that I usually hear it from amateurs who have completely misinterpreted it. It is trotted out in support of a rehearsal strategy that involves endless drill and the desire to be able to ‘do it the same every time’.
Now, I’m not knocking reliability in performance. It’s good to know that you can produce the goods in front of an audience without screwing up. I’m just questioning (a) whether drill is the best strategy to achieve it and (b) whether it is the best use of rehearsal time. After all, as Kaplan points out, the goal of rehearsal is to change things, not to make them the same.