It’s not hard to imagine a pop-psych interpretation of Adam Grant: that his generosity might have its roots in some kind of need — maybe a need he feels, even more than the rest of us, to be liked. Or perhaps that he is channeling his extreme ambition into a feel-good form of achievement. Productive and happy, Grant could even be seen as a paradigm of Freud’s definition of mental health: aggression sublimated into work.

But he has never put much stock in psychoanalysis — if the work is not data-driven, he’s skeptical. “I think a lot of it is baggage that goes back to Freud, and Freud would always say that whatever is going on with you can be traced back to something that happened early in childhood with your mother,” he told me, by phone, as he was driving to work one day. “You can either accept that or be in denial. You can’t win!” He would rather simply understand himself as someone who gets a lot out of giving, then harness that feeling, study it and see how the mechanisms involved can inspire others to succeed.

One night Grant forwarded me a grateful e-mail from a student whose life, the student said, changed because of some advice Grant gave her. I commented that most people would be thrilled to receive one note like that in a lifetime. “I get several dozen a week,” Grant said. He agreed to send some my way. That evening, at around 8:30, the e-mails started coming — Thank you for our conversation the other day and for your genius. . . . I couldn’t have done this without you. . . . I cannot thank you enough for your time and insight. . . . I’m thrilled. And I have you to thank. . . . After the first 10, I was impressed; when they kept arriving, I was surprised. On and on, until almost 11, my e-mail kept pinging; when I awoke the next morning, I saw that he had forwarded me 41 e-mails from the preceding week, each one of them numbered for my convenience.

Was this compulsive behavior? “Not really,” Grant said. “I would see it as goal-oriented and focused.” He said the question had generated a new research idea for him: “How Prosocial Behavior Can Mitigate O.C.D. Tendencies.”

Grant’s book, incorporating several decades of social-science research on reciprocity, divides the world into three categories: givers, matchers and takers. Givers give without expectation of immediate gain; they never seem too busy to help, share credit actively and mentor generously. Matchers go through life with a master chit list in mind, giving when they can see how they will get something of equal value back and to people who they think can help them. And takers seek to come out ahead in every exchange; they manage up and are defensive about their turf. Most people surveyed fall into the matcher category — but givers, Grant says, are overrepresented at both ends of the spectrum of success: they are the doormats who go nowhere or burn out, and they are the stars whose giving motivates them or distinguishes them as leaders. Much of Grant’s book sets out to establish the difference between the givers who are exploited and those who end up as models of achievement. The most successful givers, Grant explains, are those who rate high in concern for others but also in self-interest. And they are strategic in their giving — they give to other givers and matchers, so that their work has the maximum desired effect; they are cautious about giving to takers; they give in ways that reinforce their social ties; and they consolidate their giving into chunks, so that the impact is intense enough to be gratifying. (Grant incorporates his field’s findings into his own life with methodical rigor: one reason he meets with students four and a half hours in one day rather than spreading it out over the week is that a study found that consolidating giving yields more happiness.)

The studies are elaborate, the findings nuanced — but it is easy to walk away from the book forgetting the cautionary tales about people who give too much and remembering only the wash of stories about boundless generosity resulting in surprising rewards: a computer programmer who built a Web site at no cost for music fans (one of whom turns out to be an influential figure in Silicon Valley); a financial adviser who travels to take on a client thought to be impoverished (only to find that person sitting on a significant fortune); the writers who start out working free on a project for a friend (and somehow end up among the most successful in Hollywood).