You might expect those who know that death is not too far away, such as senior citizens, would be bummed out. But seniors are usually happier than younger people.
Ideas about what is a problem or simple misbehavior versus what is a clinical disorder have evolved over the past few decades. The consequences of this evolution are complicated.
Studies of how well kids are able to delay gratification when offered marshmallows yield some surprising messages about how both character and context shape behavior.