Saying thank you is ingrained in our social culture. Say thank you when someone holds the door, say thank you when someone pays a compliment, say thank you when someone gives you a gift—the list goes on. Politeness counts. Beyond just good manners though, the practice of showing gratitude has some selfish benefits, too. Research shows that even just 15 minutes of daily gratitude can dramatically decrease stress hormones in your body. Can’t make it to yoga? Crank out those thank-you notes you’ve been meaning to write for weeks now.