Sending physical letters just isn't cool anymore, and it takes too much time to print, stick it in an envelope, and walk to the store to get a postage stamp. Companies seem to really be acknowledging that and building their businesses around it.

eSnailer is the latest to the market. The interface is clean, and extremely easy to understand. Start by filling out the envelope from the fields in the top left, then move on to the recipient's field in the center, and continue with a full fledged text editor. When your letter is complete, eSnailer will print, envelope, stamp and send it via regular US postal mail, all for free.

So, what's the catch? eSnailer is ad supported. They ask that as soon as you send the letter that you accept one of the free offers you are presented with, using the address you supplied as a junk mail receptacle. Nice. Is it worth it? You decide.

NEW YORK CITY has decided to offer cash rewards to some students based on their attendance records and exam performance. Diligent, high-achieving seventh graders will be able to earn up to $500 in a year. The plan is the brainchild of Roland G. Fryer, an economist who has been appointed as “chief equality officer” of the city’s Department of Education.

The assumption that underlies the project is simple: people respond to incentives. If you want people to do something, you have to make it worth their while. This assumption drives virtually all of economic theory.

Sure, there are already many rewards in learning: gaining understanding (of yourself and others), having mysterious or unfamiliar aspects of the world opened up to you, demonstrating mastery, satisfying curiosity, inhabiting imaginary worlds created by others, and so on. Learning is also the route to more prosaic rewards, like getting into good colleges and getting good jobs. But these rewards are not doing the job. If they were, children would be doing better in school.

The logic of the plan reveals a second assumption that economists make: the more motives the better. Give people two reasons to do something, the thinking goes, and they will be more likely to do it, and they’ll do it better, than if they have only one. Providing some cash won’t disturb the other rewards of learning, rewards that are intrinsic to the process itself. They will only provide a little boost. Mr. Fryer’s reward scheme is intended to add incentives to the ones that already exist.

Unfortunately, these assumptions that economists make about human motivation, though intuitive and straightforward, are false. In particular, the idea that adding motives always helps is false. There are circumstances in which adding an incentive competes with other motives and diminishes their impact. Psychologists have known this for more than 30 years.

In one experiment, nursery school children were given the opportunity to draw with special markers. After playing, some of the children were given “good player” awards and others were not. Some time later, the markers were reintroduced to the classroom. The researchers kept track of which children used the markers, and they collected the pictures that had been drawn. The youngsters given awards were less likely to draw at all, and drew worse pictures, than those who were not given the awards.

Why did this happen? Children draw because drawing is fun and because it leads to a result: a picture. The rewards of drawing are intrinsic to the activity itself. The “good player” award gives children another reason to draw: to earn a reward. And it matters — children want recognition. But the recognition undermines the fun, so that later, in the absence of a chance to earn an award, the children aren’t interested in drawing...