It's always better to help someone than not, right?

We begin this episode in a virtual classroom. Several years ago Kellie Gillespie took an online course in social psychology, taught by Scott Plous of Wesleyan University. Hundreds of thousands of other people enrolled in the same online course.

Kellie and her classmates were exposed to psychological concepts such as the norm of reciprocity: if you're nice to someone, or you open up to them, they're likely to do the same with you. They also learned about the power of empathy: when you put yourself in someone else's shoes, the relationship you have with them profoundly changes.

The ideas in the course carried over into Kellie's life in London. Kellie was spending a lot of time at the British Library, and she often noticed the same young man on the street nearby. She could tell he was homeless. Her interactions with the man started simply, with Kellie giving him whatever spare change she had. But after a couple of months, she wanted to do more.

After we hear Kellie's story, we meet Don Laub, a surgeon who, in his words, wanted to "do a big thing, and help a lot of people."

His story is one of many triumphs — and a tragedy that he continues to dwell on many decades later.

This week on Hidden Brain,we explore two stories about people doing their best to do good in the world — and how their actions affected others around them.

Hidden Brain is hosted by Shankar Vedantam and produced by Parth Shah, Jennifer Schmidt, Rhaina Cohen, Thomas Lu, and Laura Kwerel. Our supervising producer is Tara Boyle. You can also follow us on Twitter@hiddenbrain, and listen for Hidden Brain stories each week on your local public radio station.

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