City were dumped out of the FA Cup at home by Championship Wigan.
But Hart is hoping the disappointment can be channelled into a powerful display against Champions League opponents Barcelona tonight.
He said: "To win four trophies was always going to be hard, but when you break it down, we can win every game we go into so it was a massive disappointment for us, but we can't ignore that Wigan played well.
"I think the lads who played would be the first to admit we didn't achieve our normal standards in the first half in terms of the energy and tempo we like to play at, especially in front of a sell-out Etihad crowd.
"There are no excuses but we have to learn from it and move forward, hopefully starting against Barcelona."