When's that last time you wrote a thank-you note? I'm not talking about those "thanks for your business" emails that are generated automatically or the smiley icon you use on a text to someone. I mean a real, honest to gosh, sincere thank you note. Well, if you haven't done one of those in a while, you might want to reconsider because researchers have shown that the simple act of writing a sincere thank you note has all kinds of physical and psychological benefits, both for the sender and the person who receives it.