Succinct and finely tuned thoughts on why happiness has little to do with money, youth, or even education, by the director of the MacArthur Foundation Research Network on Successful Mid-Life Development. Humans make themselves happy, Brim argues, by finding a ``way to live at the level of just manageable difficulty.'' He begins this clearsighted meditation on ``human nature and ambition'' with the example of his father, who left teaching at 60 and set his ``unyielding drive for growth and mastery'' on clearing hundreds of acres of wood. This contented man pursued this challenge until physical limitations stopped him; then he turned to a garden and, finally, a window box. Whatever scale the challenge, humans use ``the same operating energy.'' After successes or failures, we adjust. Not only can people change (``the course of human development is much more open than used to be believed''), but ``the true capacities of a person are often inherently unknowable.'' On the other hand, we may have more trouble abandoning goals than behavior, and we may misread the probabilities for a second chance. Such generalities come across here as convincing because they evolve from logical argument supported by psychological theory and by examples ranging from the musicians in second-tier orchestras dealing with their status to foundation directors frustrated because they can't get ``hard information'' about their success. What Brim plainly and most disturbingly sees is that this country does not support those losing ground in their careers. With economic troubles all around and fortunes gone sour overnight, Brim forsakes the quick fix for thoughtful observations about how we drive ourselves and measure results.