Descartes looked inward for truth. This was his famous use of "Cartesian doubt" to deny the reality of the external world. In doing so, Descartes ultimately grounded truth in the self with his "cogito, ergo sum." I think, therefore I am.
Freud looked inward for mental health. Deep in our unconscious, said Freud, dwelt the secrets and roots of our neurosis. If we could delve inside ourselves to locate and untangle those unconscious knots, we would emerge from the cave of the self healthier and happier. The impact of this psychoanalytic advice upon the modern world has profoundly shaped our cultural assumptions regarding mental health. Today, mental health is broadly assumed to be achieved through psychological spelunking, going inside to "figure myself out."
As I describe in The Shape of Joy this inward turn, the collapse of the self, has had deleterious effects upon our well-being. Research over the last few decades has pointed out how excessive self-focus, introspection, and rumination is bad for us. It is not good to be alone in your head. As the psychologist Ethan Kross describes in his book Chatter:
“In recent years, a robust body of new research has demonstrated that when we experience distress, engaging in introspection often does significantly more harm than good. It undermines our performance at work, interferes with our ability to make good decisions, and negatively influences our relationships. It can also promote violence and aggression, contribute to a range of mental disorders, and enhance our risk of becoming physically ill.” (emphasis mine)In The Shape of Joy I also discuss research on the "default state" of the mind. That is to say, what does the mind do when it has nothing to do? Nothing to focus on or occupy itself? The answer is that the mind wanders. In a 2010 study published in Science it was discovered that 47% of the time our mind is wandering. We're simply not mentally present. Ponder that. We spend half our lives lost within ourselves. And that same study showed how this mental wandering is associated with unhappiness. As the researchers succinctly state, "A wandering mind is an unhappy mind."