One day when going to check on my friends’ status updates on Facebook, this jumped out at me:

Attention Facebook friends: Please for the love of God stop sending me gifts and invites for Farmville, Mafia Wars, Vampires, and whatever other crappy THING you’ve been playing. DO NOT WANT. Just …STOP. GOD.

Those of you on Facebook or MySpace can probably sympathize. How many times have you checked your notifications and thought “Gee, you sent me a …virtual goat. THANKS. I guess. Guess I should click on your link.” Indeed, developers of these social games have gone to great lengths to make “gifting” of imaginary stuff a core element to the gameplay, and they’re even starting to offer pixilated gifts for real money. Why is that? Why do people do that?

The answer has to do with one of the most powerful habits in social psychology: the reciprocity effect. When people give you something, you feel the need to give something back; it’s that simple. Or possibly if you’re like my friend quoted above, you yell at them. But usually you want to reciprocate. Some evolutionary psychologists think that this is an evolutionary advantage in that it encourages societies to form –and enforce– mutually beneficial norms. Adhering to the norm is seen as a good deed, and others want to return that deed; breaking the norm is an attack, and will earn you a misdeed in return, like shunning or a punch to the neck.

Thank you for the sheep, Guy I Knew in High School.

The reciprocity effect is put to use by marketers and savvy businesspeople all the time. Every year the March of Dimes charity sends me a lovely set of return address labels for use with my Christmas cards 1. The labels are a free gift, but not coincidentally, they come in the same envelope as a plea to donate. The message is clear: “Dude, we totally just gave you some free stuff. You should return the favor with a donation.” Psychologist Robert Cialdini explained in a 2001 article in Scientific American how the Disabled American Veterans organization used this same trick to increase the success rate of their appeals for donations from 18% to 35%. 2

The same technique is used by supermarkets giving you free samples of new cheese crackers, or the video game developer who gives out free tee shirts to the press or buyers during a trade show. I’m not saying that you’ll be mind controlled and compelled to return the favor by buying the crackers or giving a favorable writeup, but you’ll at least think about it more than you would have otherwise. Many organizations even invoke “no gifts” codes of conduct to guard against things like the reciprocity effect.

But what about Farmville? That’s a free game, right? And most of the gifts are free, too, right? For the most part, but Zynga, the makers of Farmville and other social games like Mafia Wars, nevertheless want new players to come in and existing players to stick around. The gifts in these games are useful to their recipients within the game, so seeing a notification that you’ve gotten one encourages you to log into the game and put it to use. And actually just clicking on the link will start you down the path to installing and playing the game, which increases Zynga’s numbers. Then the reciprocity effect then encourages you to return the favor by sending a gift back, which creates a cycle of reciprocating fruit plants, livestock, and penguin statues flying back and forth. Even worse is when you realize that if you DON’T perpetuate the gifting loop, you’ll hurt your friends by making them waste in-game money for things they were hoping to get from you as gifts, you heartless bastard.

This is an effective mechanism for getting people to perpetually log back in to Farmville, for example, instead of moving on to other games. There’s the notification telling you that you need to log in to reciprocate the gift, and while you’re there you might as well play for a while. You can even send gifts to people who don’t play the game yet, encouraging them to pay you back by starting up a game as your neighbor or teammate. Farms everywhere in an unholy amalgamation of psychology and agriculture!

But wait, there’s more. The real money for companies like Zynga comes when you feel compelled to spend REAL money to reciprocate a “premium” gift. In fact, let’s see what Mark Pinkus, CEO of Zynga, had to say in a recent interview with Charlie Rose 3

We are excited about the future of social games and virtual goods as a revenue model within social games. What I mean by that is …these are free games, and one to two percent of the users will spend money in the games. And they can spend it on virtual goods, virtual gifts we just started selling, and that has been a revenue model that has enabled our company to be profitable for eight straight quarters.

So, enjoy your free sample. But don’t underestimate its effect on you.