When you don't have hair and you need some so you take a sharpie and draw in a tiny patch of hair to cover your bald spot.
"Hey Craig, I know how to solve your hair loss problem!"
"How?!"
"Just use this sharpie and draw in a patch of hair on the middle of your head."
"Gee, a patch?"
"Yes, a patch! It's also called a sharpie patch because it makes you look like you have hair!"
"That's a great idea!"