Dental Hygiene is very important

Dad: "Trevor, go brush your teeth."
Trevor: "Why?"
Dad: "Go brush your teeth."
Trevor: "Why?"
Dad: "Go brush your teeth, and I'll tell you when you're done."

Trevor padded off to brush his teeth.

Dad to Mom: "Wow. I'm surprised that worked."

Trevor to Dad after brushing his teeth: "Why did I have to brush my teeth?"