Someone holds the elevator for you. No “thank you”? You end up waiting in the lobby next time. You spend all weekend helping a friend move and at the end of it, all they say is, “Well, I’ll see you around.” Looks like someone just made your Nixon-esque enemy list.

Those two simple words could be the difference between a functioning society and an admittedly exaggerated chaos, but even if that chaos is exaggerated, there are plenty of reasons to remember to say “thank you.” Here are just a few.

You’ll Make More Money

It’s true. There are economic benefits to be gained by merely expressing gratitude. Don’t buy it? Check out this study about how waiters who write “thank you” and personalized messages on receipts get larger tips than their less...