“Fantasizing about a world without low mood is a vain exercise. Low moods have existed in some form across human cultures for many thousands of years. One way to appreciate why these states have enduring value is to ponder what would happen if we had no capacity for them. Just as animals with no capacity for anxiety were gobbled up by predators long ago, without the capacity for sadness, we and other animals would probably commit rash acts and repeat costly mistakes. Physical pain teaches a child to avoid hot burners; psychic pain teaches us to navigate life's rocky shoals with due caution.”