happiness is generated from external stimuli or reflecting on the memory of those stimuli. Each person will have diffrent happy responses to diffrent stimuli and the degree of happiness will also fluctuate. In this lies the fatal flaw of happiness. For example having your first child well most likely make you more happy then your favorite team winning a game. If having your first child is the happiest event in your life you will measure all other happy responses to that event (on some level atleast) in effect to some degree the level of happiness achieved is diminshed by prior happy causing events. This leaves you, in your pursute of happiness, forever chasing the happiest event which of course is unattainable because it will never be the same as the first time. Eternal happiness can not exist as you would always be needing to make new highs. Contentment on the other hand can be achieved.