How does all this work? One explanation is that acting happy, regardless of feelings, coaxes one’s brain into processing positive emotions. In one famous 1993 experiment, researchers asked human subjects to smile forcibly for 20 seconds while tensing facial muscles, notably the muscles around the eyes called the orbicularis oculi (which create “crow’s feet”). They found that this action stimulated brain activity associated with positive emotions.

If grinning for an uncomfortably long time like a scary lunatic isn’t your cup of tea, try expressing gratitude instead. According to research published in the journal Cerebral Cortex, gratitude stimulates the hypothalamus (a key part of the brain that regulates stress) and the ventral tegmental area (part of our “reward circuitry” that produces the sensation of pleasure).

It’s science, but also common sense: Choosing to focus on good things makes you feel better than focusing on bad things. As my teenage kids would say, “Thank you, Captain Obvious.” In the slightly more elegant language of the Stoic philosopher Epictetus, “He is a man of sense who does not grieve for what he has not, but rejoices in what he has.”

In addition to building our own happiness, choosing gratitude can also bring out the best in those around us. Researchers at the University of Southern California showed this in a 2011 study of people with high power but low emotional security (think of the worst boss you’ve ever had). The research demonstrated that when their competence was questioned, the subjects tended to lash out with aggression and personal denigration. When shown gratitude, however, they reduced the bad behavior. That is, the best way to disarm an angry interlocutor is with a warm “thank you.”

I learned this lesson 10 years ago. At the time, I was an academic social scientist toiling in professorial obscurity, writing technical articles and books that would be read by a few dozen people at most. Soon after securing tenure, however, I published a book about charitable giving that, to my utter befuddlement, gained a popular audience. Overnight, I started receiving feedback from total strangers who had seen me on television or heard me on the radio.

One afternoon, I received an unsolicited email. “Dear Professor Brooks,” it began, “You are a fraud.” That seemed pretty unpromising, but I read on anyway. My correspondent made, in brutal detail, a case against every chapter of my book. As I made my way through the long email, however, my dominant thought wasn’t resentment. It was, “He read my book!” And so I wrote him back — rebutting a few of his points, but mostly just expressing gratitude for his time and attention. I felt good writing it, and his near-immediate response came with a warm and friendly tone.

DOES expressing gratitude have any downside? Actually, it might: There is some research suggesting it could make you fat. A new study in the Journal of Consumer Psychology finds evidence that people begin to crave sweets when they are asked to express gratitude. If this finding holds up, we might call it the Pumpkin Pie Paradox.