Every difficulty slurred over will be a ghost to disturb your repose later on.
He was thinking of it in terms of life in general, but I replied with a musical application:
It is very true in a practical sense for music. I experienced it myself this morning. I decided to play as a postlude the Bach E minor fugue we had discussed. I struggled with the subject's entrance in the pedal when I learned the piece almost 30 years ago, and I still struggle with it today! My pedal technic is not as good as my hands', and because of that I never feel really secure in that spot. Even worse with such passages, if you don't immediately isolate them, work them slowly, in hands/feet combinations, different articulations, literally backwards and forwards, with innumerable repetitions, to ensure security -- worse yet, if you just blunder through them as you play through the neighboring, easier sections -- you will never be mentally secure on them. Thus, even if your hands and feet "know" the passage, your mind will always flinch as you come upon it. And that will be your downfall. Your hands and feet cannot do anything that your mind objects to, and your mind will object as you try to play a poorly-prepared passage.The reality is that I *am* able to play the passage, but it's still a place of concern. Steady, thorough preparation is crucial to secure musical performance. I guess that could be applied to life as well.