I saw this quote on a forum and it's worth repeating:
"Amateurs practice until they can play something right…
Professionals practice until they can't play it wrong"
That very succinctly describes the difference between learning something to where you can play it okay on a good day compared to imprinting it into your brain so fully that you can play it well on a bad day. I have too many songs that fit into the first category and not enough in the second. Better practice some more…