When I was little, whenever I felt something wasn’t fair, and I went and complained to a parent or teacher, etc., and got a “well, life’s not fair!”, that response always bothered me. I would reply, “Yeah, life’s not fair, but the whole point of everything we do is to work towards making it as fair as possible, so ‘life’s not fair’ is just a cop-out, it’s you saying that although you recognize that this situation isn’t fair, you just don’t care enough to do anything about it.”
I’ll remember this in case I ever end up with kids someday, so I can respond more diplomatically when I really don’t care enough to do anything about it.