Just sharing because I'm amused by this. Sometimes you come across something that highlights what you might call a blind spot, or perhaps an aspect of your way of thinking you aren't aware of. I'm usually above average when it comes to playing by ear and improvising solos. I'm not great or amazing, I'm just saying that I seem to find that easier than most players I've played with and playing sort of flows. But occasionally I'll come across a rythmn or phrasing that inexplicably stumps me. In this old surf number (the last one to chart before the Beatles changed everything, incidentally) the middle 8 is very simple, but for some reason I have to really concentrate to play it or I mess up. Some aspect of it confuses my head and my fingers want to do something else.