When I was over-concentrating instead of letting it flow naturally. I first approached "Butterfly" from Jason Mraz and "Billy Jean" from Michael Jackson and didn't think I'd be able to play the chord changes, keep the time, and sing the words without the whole thing train wrecking...
The slow, methodical, practice helped with my fingers remembering the chord shapes, but then it was taking all of that and putting in the pocket... let the song play without over thinking it. That makes room for the brain to concentrate on lyrics and groove.