If you’re about to walk into a bar with you head, or like the top of a doorpost or smt. You’ll instinctively pull back and avoid the obstacle, inches before it hurts, because your brain notice the hairs on your head moved. That’s why men who have recently gone bald, often have bumps and bruises on their head. My bald colleague told me that for him, that was the hardest thing about going bald.