Small acts of kindness are sometimes powerful enough to make major headlines. In fact, you’ve probably read about or watched stories unfold about this. Here’s how it usually plays out: One person will do a good deed— such as giving a cup of coffee to a homeless person, or giving up there seat on a busy train to someone less able than themselves—and this will start a trend, with more and more people getting in on the act. The result is a feel-good story for all. The benefactors are happy to have done a good deed and the recipients are pleased to have been given a small but meaningful helping hand.

However, the circle of generosity doesn’t end there—in fact, it’s exponentially bigger. Recipients of kindness generally want to keep paying it forward and a single act of kindness typically can inspire several more acts of generosity. The scientific name for this chain of altruism is “upstream reciprocity,” but you can think of it as a domino effect of warm and fuzzy feelings: If you offer your unexpired parking ticket to someone who is about to park, the recipient of that small act of generosity will be inspired to do thew same to someone else, and on and on.

The Helper’s High

So where do these good feelings come from? When you are kind to another person, your brain’s pleasure and reward centers light up, as if you were the recipient of the good deed—not the giver. This phenomenon has actually earned the nickname “helper’s high” among psychologists who study generosity, and some researchers theorise that the sensation is also due to a release of endorphins, the feel-good chemicals in the mind. It’s no surprise then that happiness research found that people who are altruistic—in this case, people who were generous financially, such as with charitable donations—were happiest overall.

Of course, part of why giving feels good is because we know we’re lifting someone else’s spirits . Receiving a gift, assistance, or even an encouraging smile activates the brain’s reward center, a phenomenon that’s hard to explain but easy to feel—just think back to the last time a stranger held the door for you or your partner surprised you with your favorite meal. The sudden appearance of these positive feelings is what helps keep the giving chain alive: Somebody who has just received any act of kindness is elevated, happy, and grateful, making them likely to help someone else.

But there’s more. The effects of kindness can be so great that you actually don’t have to be directly linked to a giving chain to get in on the act. By simply witnessing generosity you may be inspired to do something generous of your own, according to new research which found that simply observing kindness can spur more acts of good. Humans often mimic behavior they see, and that includes generosity, which explains why some of these stories of small acts of kindness become bigger news: Even people who simply hear about a giving chain are often inspired to give, starting a chain of positivity all their own.