Have you ever felt like that? That some boss or some area at some game seems like impossible, then you totally forget about it, later you grab the game just because and bam, you win.
I remember when I was fighting Astaroth in Viewtiful Joe 2.
I lost that boss battle 15 (yes, I counted) times.
I snapped on the 16th try and beat him, no damage.
Not nearly as hard as Fire Leo's brother(whatever his name is)though. That bastard was insane.