G.B.
It is a skill he will learn much faster when he isn't resentful at someone and that energy being directed at them is not going to processing his environment....let me see if I can say that differently.
If he is focused on a person and his brain is not able to move on he is not processing what he needs to learn from the experience. He is not able to.
I would say hubby needs to back off and let him learn on his own. If it runs out it is out, no reminders, nothing. I am a helicopter parent and know from experience the more I let the kids go the more they learn.