By Dylan Selterman - Dylan Selterman is a lecturer in the psychology department at the University of Maryland and editor-in-chief of In-Mind magazine...

Imagine you're a student and your teacher poses this challenge to the entire class:

You can each earn some extra credit on your term paper. You get to choose whether you want 2 points added to your grade, or 6 points. But there's a catch: if more than 10% of the class selects 6 points, then no one gets any points. All selections are anonymous, and the course grades are not curved.

I pose this exact challenge to students each semester in my social psychology course at the University of Maryland. This summer, one of my students happened to tweet about it, and his reaction went viral. This puzzle has resonated with millions of people around the globe—in the past week I've gotten responses from people in Poland, Spain, Italy, Croatia, New Zealand, and Paraguay, to name a few.

This exercise impels students to consider how their actions affect others, and vice versa. I've been giving it to students since 2008, and only one class has successfully mastered the challenge. In all other classes, more than 10 percent chose 6 points. Students' temptation to reach for more points is very strong, and they often express exasperation when things don't go their way. Last semester after I announced the results, one student threw up her hands and emphatically said, "If only everyone chose 2 points, we all would have gotten the points!"

Many professors in my field use versions of this exercise, which was first developed 25 years ago. I learned it as an undergraduate studying psychology under Steve Drigotas at Johns Hopkins. (I chose 2 points, and watched with extreme frustration as those points were lost when too many of my classmates choose 6 points.) As climate change and population growth threaten our resources, the experiment is more relevant now than ever.