I’m reading a terrific book addressing this question — Freedom to Change by Frank Pierce Jones, a professor of Classics at Brown University and a teacher of Alexander Technique.
Happiness is defined as “doing well something that interests you.” It can be seen at its clearest in a healthy child at play whose pleasure resides in the satisfaction of making something work. This satisfaction, Alexander says, can be established even more strongly when the mechanism that is made to work is the child’s own. Here he describes vividly the change in facial expression and the look of pleasure that a child shows when he suddenly discovers in a lesson that he can do easily and in a coordinated manner something he has always done awkwardly before, realizing, for example, that he can in this way improve his skill in games. “It’s a happiness,” Alexander said, “which increases with the psycho-physical improvement.” In marked contrast is the unhappiness shown by most adults as they approach middle age and realize that they are not improving in themselves but deteriorating. Success is essential to happiness in everyone. When happiness cannot be obtained in the ordinary way, in the satisfaction of using oneself optimally in the routine of everyday life, a person will begin pursuing specific pleasures. People unfortunately have been taught to make the routine activities of daily life automatic and as far as possible unconscious. This leads to a condition of stagnation and the harmful demand for specific excitements and stimulations, none of which can possibly produce real happiness. Such happiness can only be obtained by restoring to a person his own sensory standard so that he can gradually re-establish a pattern of growth and self-satisfaction that will carry him beyond middle age and into old age. Happiness, then, consists in the sensory satisfaction that comes with an increase of self-knowledge and control. This satisfaction extends to all aspects of living (including, of course, the sexual).