They multiply and you can't keep track of them. They constantly get lost, and even if you find them you can't keep them where they belong! They poop constantly. (OK, so socks don't actually poop, but they all have holes where something comes out!) And as much as you love them, you wish you could get rid of them!!
One of the maladies of having many young children is the fact that they must wear socks! I spend the winter attempting to keep non-holey socks on five children. It's an exhausting task. One that requires more than I can give. So my children are constantly wearing mismatched holey socks. It doesn't matter that I just bought everybody big bags of socks. No, they are still holey. And they disappear! I swear there's an alternate sock universe out there with all the lost socks. And they are standing there laughing at the efforts to find them, knowing that they will never be found!!