Matthew D. Lieberman

Psychologically, our reality derives from the stories we tell ourselves, at least the ones we believe.

If a stranger saying we are "dependable" activates the reward system, imagine what praise from a boss, a parent, or even an unaccomplished slightly older graduate student will do. Of course, we all know that praise is a good thing, as long as it isn't too unconditional, but until very recently, we had no idea that praise taps into the same reinforcement system in the brain that enables cheese to help rats learn to solve mazes. And positive social regard is a renewable resource. Rather than having less of something after using it, when we let others know we value them, both parties have more.

The fact that mammalian crying serves as a cue for maternal support, rather than as a dinner bell, is a major evolutionary difference.