For my youngest son, it is a physical impossibility to not touch something once he's decided that he wants to touch it. Impulse control issues, I suppose. He can know before he touches something that he shouldn't, that he'll get in trouble for touching it. He can't stop himself. He'll even say as he reaches to touch it that he knows he shouldn't. Yet he does it anyway.
This morning, he was touching everything on the bathroom counter. Everything. Not making a mess, just touching everything. I spelled, "quit m-e-d-d-l-i-n-g-!" And he said, "I'm not meddling!" He knew what I'd spelled, what I was saying by my tone of voice, because as brilliant as he might be, he barely knows the difference between red and green, much less how to spell anything.
Impulse control issues. Just like his mother in the Halloween candy.