Q: Why did you do that? (mistake, error)
A: Well someone had too.
A: God made me.
A: Don't hate me!
A: My mistake, not the end of the world.
Q: Why didn't you do that? (homework, cleaning, etc.)
A: I had higher priorities.
A: Well you see, I forgot, but I won't let it happen again.
A: No one said I had to. Never heard of it.
A: *runs*