"In particular, Vaillant says, it is the experience of loving and being loved that most closely predicts how we react to the hardships of life; human… - Jonah Lehrer

When the mind is denied the emotional sting of losing , it never figures out how to win.

How do we regulate our emotions? The answer is surprisingly simple: by thinking about them. The prefrontal cortex allows each of us to contemplate his or her own mind, a talent psychologists call metacognition. We know when we are angry; every emotional state comes with self-awareness attached, so that an individual can try to figure out why he's feeling what he's feeling. If the particular feeling makes no sense — if the amygdala is simply responding to a loss frame, for example — then it can be discounted. The prefrontal cortex can deliberately choose to ignore the emotional brain.

But the physical health of these young monkeys hid a devastating
sickness: they had been wrecked by loneliness. Their short
lives had been defined by total isolation, and they proved incapable
of even the most basic social interactions. They would maniacally
rock back and forth in their metal cages, sucking on
their thumbs until they bled. When they encountered other monkeys,
they would shriek in fear, run to the corners of their cages,
and stare at the floor. If they felt threatened, they would lash out
in vicious acts of violence. Sometimes these violent tendencies
were turned inward. One monkey ripped out its fur in bloody
clumps. Another gnawed off its own hand. Because of their early
deprivation, these babies had to be isolated for the rest of their
lives.