If he hasn't learned that by now(3 seasons), I'm afraid he never will. He always makes the same errors time and time again and again.
Since his first season he has barely progressed at all, and I think it has to do with his football intelligence. He is the opposite to Naismith.
Barkley is the same player that he was three years ago and I can't see him becoming a better player than he is at the moment.
He's fast, he's got good technique, he's strong, he can run with the ball, he has a powerfull shot, he is good at set pieces, he's got tons of natural talent but he isn't intelligent.
The thing is british football fans love a player that runs around like a headless chicken and Barkley is this kind of player.