Same Difference

Today, while eating lunch - Peter asked Tim what 'why not?' means?
And, the conversation went something like this. . . .

Peter: What does 'why not' mean, Dad?
Dad: Well, it's kind of like saying 'yes'
Peter: *silent*
Dad: It would be like you asking me something, like if you asked if I was your Dad, and I would say . . . . . um . . . . .

{dramatic pause . . and careful consideration of a GOOD example to give}

Dad:. . .It would be like if you asked me for something to drink, and I would say 'why not' - meaning 'yes'!