When undergraduate Mason Jenkins read Dan Ariely’s best-selling book, Predictably Irrational, he wasn’t overly impressed with the chapter titled “The Cost of Zero-Cost,” in which Ariely wrote about how pricing chocolate in slightly different ways showed how utterly irrational people are about free stuff. Jenkins found it curious that Ariely chose chocolate for his experiment. Would people make different decisions if offered other stuff? Jenkins took to the Pit on UNC’s campus to find out.

In Ariely’s book, he explains a simple experiment he did at MIT. He asked one hundred students if they would prefer to buy a Hershey’s Kiss for one cent or a Lindt truffle for fifteen cents. (Understood, here, is that Hershey’s is lower-quality chocolate than Lindt.) Seventy-three percent of the students bought the truffle. When each item’s price was reduced by one cent, the Kiss became free and the results changed dramatically. Sixty-nine percent chose Hershey’s and 31 percent bought the truffle. Ariely calls this decision-making irrational. The difference was a single penny!

The best explanation Ariely can offer is that because humans are intrinsically afraid of loss, they irrationally choose a free item,” Jenkins says. It’s the rarity of acquiring something for free, the promise of a unique and effortless gain that makes us choose the free item. So goes the theory of zero-cost.

Jenkins wanted to see what happened when people were offered something other than cheap chocolate. In one experiment he asked one hundred UNC students if they’d prefer a five-day trip to Hawaii for $700 or a two-day trip for $300. Eight-six percent picked the more expensive trip. After all, it was the better deal. But when the prices were lowered three hundred dollars—when the cheap trip became free—43 percent chose the $400 trip and 57 percent chose the free trip. A similar flip happened when Jenkins asked students to choose between a cheap and expensive cruise, or between a free cruise and a cheap one.

But choices between other products led to strange results.  For instance, when Jenkins asked students to choose between a one-dollar cheeseburger from a fast-food joint and a seven-dollar hamburger from a more upscale restaurant, 46 percent chose the cheap meat. When the fast-food burger became free, student preference didn’t change—46 percent chose the free burger.

When it came to shoes, Jenkins found that students shunned the cheap or free generic brand. Fifty-one percent chose the high-priced ($60), brand-named shoes and 49 percent chose cheap ($20) generic shoes. When the cheap shoes became free, only 45 percent of students opted for them. He got a similar result with motels. When offered the choice between a cheap motel room ($40) and a more expensive room ($100), just 59 percent chose the cheap room and 41 percent chose the more expensive room. But when the $40-room became free, only 45 percent chose it; 55 percent chose the $60 room.

To Jenkins, the motel question speaks volumes about how rational human decision-making can be. “Overnight safety and security are vitally important,” he says. The more expensive motel is in an upscale area of Chapel Hill. The lower-priced room is located in a dimly lit area near the Interstate. Both motels are the same distance from campus.

Jenkins didn’t stop there. He broke down his results into male and female respondents. Men were twice as likely as women to pay for the longer cruise to Hawaii rather than take the shorter, free trip. Males were more likely to choose the higher-priced cheeseburger over the free burger. But women were more likely to choose the more expensive burger than the one-dollar burger. When it came to shoes, you guessed it: men preferred the free shoes. Women preferred the higher-priced shoes to the lower-priced shoes. And when the cheap shoes became free, women were even more likely to choose the expensive shoes.

These results add layers to Ariely’s initial research,” Jenkins says. And they support Jenkins’s hypothesis that gender and the types of items for sale have substantial effects on the choices we make.

Jenkins thinks that irrationality plays a role in our decisions. But he says that humans aren’t wired to make the same sorts of decisions no matter the situation or product involved.

I think it’s more productive to think of zero-cost as a situational phenomenon,” he says. “It’s helpful to pick up a free pen rather than to buy one. On other occasions, it’s better to pay more for a higher-quality computer, refrigerator, or sofa. Where I think Ariely falls short is that he only thinks of things in strict use-value terms.”

Jenkins points out that life is not about vague, general problems. Our brains have evolved over time to make decisions differently depending on the circumstances.

And that’s why the students Jenkins interviewed didn’t always leap at the free stuff. Life isn’t like a box of chocolates.

Mason Jenkins is a dual psychology and English major in the College of Arts and Sciences.