It’s not every day you get a chance to learn something from a final exam, much less one of its extra credit problems. But we’re pretty sure no extra credit problem has ever driven a point home this hard. The question, which University of Maryland psychologist lecturer Dylan Selterman has been giving on his final exams since 2008, has stumped all of his classes except one.

So what was the problem? Trying to find meaning in an inkblot? Trying to hold out on eating a marshmallow? No, but, like those famous psych tests, this does have roots in psychological concepts.

The much-debated “problem” starts off simply enough, with students being told to, “select whether you want 2 points or 6 points added onto your final paper grade.”

So far so good. But it gets a little more complicated after that. The e-mail continues, “If more than 10% of the class selects 6 points, then no one gets any points. Your responses will be anonymous to the rest of the class, only I will see the responses.”

The question was tweeted by University of Maryland junior Shahin Rafikian earlier this month and has gone viral, with over 6,000 retweets and 5,000 favorites. His accompanying caption was “WHAT KIND OF PROFESSOR DOES THIS.”

The answer: a professor who’s dedicated to his subject. According to BuzzFeed News, Selterman said that “the purpose of the question is to reinforce social psychology concepts like ‘tragedy of the commons’ and ‘the prisoner’s dilemma.’” The first concept refers to people taking up common resources for the benefit of themselves and acting contrary to the best interests of their group. The prisoner’s dilemma is a concept that tries to explain why two people might not cooperate even if it’s in their best interest to do so.

A student told ABC 7 News, “When I was an undergrad in his class, I chose the lower point option and was very upset with my peers for choosing the higher point option!”

This extra credit problem neatly tied together both concepts, and the fact that only one class—which Selterman calls an “outlier”—has managed to beat it in seven years proves an important psychological point about collective and individual selfishness. This year, like most years, more than 10% of the students chose the six-point option and no one got extra credit.

And what does Professor Selterman have to say about this? Well, he seems pretty chill with the amount of attention his “assignment” is getting:

On the plus side, everyone learned something they won’t be forgetting in a hurry. And maybe that makes this “extra credit” assignment pret-ty genius.

(Image via Twitter)