Connor (source)

The brain can be a tool. It can recall phone numbers, solve math puzzles, or create poetry. In this way, it works for the rest of the body, like a tractor. But when you can't stop thinking of that math problem or phone number, or when troubling thoughts and memories arise without your intent, it's not your brain working, but your mind wandering. Then the mind controls you; then the tractor has run wild.