We do not need big psychological theories or theses basically the following three can and does cause depression and disappointment they are CARELESS COMPARISON, CUT THROAT COMPETITION AND CANTANKEROUS CONFRONTATION and they must be replaced with compassion, co-operation and conscious care for everyone and environment around.
"An array of coordinated genes is required to explain even the minutest human phenomenon. 'Discoveries' of a 'gambling gene' here and an 'aggression gene' there are derided by the more serious and less publicity-prone scholars. Yet, it would seem that even complex behaviours such as risk taking, reckless driving, and compulsive shopping have genetic underpinnings."
The Selfish Gene – The Genetic Underpinnings of Narcissism