Sisters. They're great for having built-in best friends, chatting all night, and of course, "borrowing" clothes. My sister and I are definitely all of that for each other, and in fact, that's the case for all of the sister duos and trios in my life. If you have a sister, you probably know just how special they are. Whenever you need a shoulder to cry on or a listening ear, they're always there.And as it turns out, studies show that having a sister could actually make you a better human being!