Ceramic knife Puns

My older sister recently had a new roommate move in and found that roommate to be a bit careless with shared items. She had recently just bought new ceramic knives and came home to find one of the tips broken off. Lamenting to my dad when she came home to visit she exclaimed "$80 knife I just bought is already broken", slamming the broken knife down on the counter.

My dad without missing a beat, looks up from his book, straight faced and says "Well, this is why you can't have knife things."