“Sometimes your joy is the source of your smile, but sometimes your smile can be the source of your joy.”

The Nobel Prize–winning psychologist Daniel Kahneman demonstrated in research that, compared to other activities, parents do not generally enjoy spending time with their children. One of the reasons for this is that parents are distracted by other activities or people, and when their attention is divided they find the experience strenuous and

There is much research on what psychologists call equity theory, which shows that most people have the need to reciprocate what they get from others; in fact, most of us feel discomfort when we’re unable to give back something of equal value. This applies to material things, like a gift or money, as well as to nonmaterial things like kindness or

Roy Baumeister, a world-renowned social psychologist, wrote similarly about the need to belong—about our fundamental and innate need to form interpersonal relationships, to maintain social bonds, to be part of a shared community.

There is a lot of research in psychology on substituting emotions—replacing anger with empathy or stress with excitement. For example, psychologist Joe Tomaka helped students with documented test anxiety to see an exam as challenging—rather than threatening—and as a result they became calmer, more creative, and performed better. Substituting a word

We should learn to pick our battles better—sometimes it’s appropriate and right to get angry or upset, but sometimes, usually in fact, it’s just not worth it.”

“That often the best way to solve problems is to do nothing.” He paused, focusing on trimming my sideburns, before proceeding: “Most people, when they face a problem, become obsessed with solving it. This is sometimes good, but usually when we just do nothing and let nature take its course, problems either resolve themselves or the solution becomes

Montessori’s idea is a variation of a famous philosophical principle called Occam’s razor. William of Occam, a fourteenth-century English philosopher, argued that in coming up with a theory, we have to make things as simple as possible and as complex as necessary.

Aristotle pointed out that friendship and contemplation are the two pillars of a happy life. We are social animals and we are rational animals—we need friends, and we need to learn. Aristotle was so convinced of this truth that he founded a school of philosophy at the Lyceum, a place where people could cultivate friendships and learn new things at