In Patti Digh's book Creative is a Verb, she describes a time when her husband asked a doctor who had worked with children for 50 years what was his biggest lesson learned about kids. The doctor replied quickly: "Never, never interrupt a child when a child is speaking to you."
Any time you allow a child to get away with a certain behavior, the message you're sending is that the behavior is OK. If there are no real consequences to his actions, all he can assume is that what he did is OK and he can get away with it.
Age sometimes seems to rob us of the ability to say what we really want to say. Coming from us, it would sound hurtful, mean, or just plain irritating. From our daughter, even now, it's refreshingly honest.