I just have to say, one of my most favorite motherhood accomplishments is winning the "Why?" battle with Luke without having you use the phrase "just because".
For example, here is our conversation prior to bed time last night:
M: "Luke, do you want to wear your basketball shorts or your gym pants to bed?"
L: "umm...train jammies"
M: "ok remember that wasn't an option?"
M: "because they are dirty"
M: "because you have worn them the last 4 nights in a row"
M: "umm probably because you love them"
M: "i don't actually know why, maybe they make you feel like a grown up because they have that cool collar and the shirt buttons up"
L: "oh. umm gym pants."
M: "thank you, and i win."