I will echo Mark’s comment here about “perfect practice” as opposed to plain old “practice”. I used to play in a classical guitar orchestra a few years back (yes, they do exist!) ;) and I was in the third guitar section, which was the most boring section as we just laid down the basic rhythm and not the flashy stuff that the first and second guitar sections did.

To alleviate boredom, we started to embellish our parts a little — especially at the end of one piece, we would all do a little silly trilly bit purely to annoy the other sections. Our conductor admonished us for this, saying that if we did that in practice, we would do it in performance. We scoffed at the ridiculousness of this idea.

Then came the big day of our first major concert, and we played through our repertoire flawlessly and with gusto, and at the end of this particular piece, all of us — and I mean all 5 of us in the third guitar section, did the trill. We looked at each other disbelievingly, but that was nothing compared to the scathing look our conductor was giving us…