Selye proposed a unified non-specific approach to many causes of death. He demonstrated that stress decreases adaptability of an organism and proposed to describe the adaptability as a special resource, "adaptation energy". The animal dies when this resource is exhausted. Selye assumed that the adaptability is a finite supply, presented at birth. Later on, Goldstone proposed the concept of a production or income of adaptation energy which may be stored (up to a limit), as a capital reserve of adaptation. In recent works, adaptation energy is considered as an internal coordinate on the "dominant path" in the model of adaptation. It is demonstrated that oscillations of well-being appear when the reserve of adaptability is almost exhausted.