And yet you felt the need to reply so passionately.

Look, who gives a fuck about teenage depression? It's so 1995! And it happens. Physiologically speaking, one just wouldn't be a "average/normal" teenager if they weren't all mopey and depressed. Their brains are being rewired and they begin feeling new sensations/emotions. All of which, are like a drug in that it's new, it's different, and it's something to experience. Ever wonder why most teenagers fall in love ever so hard? Because they never fuckin' felt that type of emotional state before! Same thing with depression! So who gives a rats fuckin' ass?! Why don't you add something philosophically profound to the conversation? Such as:

Happiness is the emotionally-symantic definition of a feeling that is derived from certain chemical states (such as endorphines) within the "physical" brain which is a direct result of a particular stimuli (in this case, being rewarded for a job well done).

OR:

Happiness is the link between one's own self (that is: his own peculiar subjective quality to the objective question of: what is a man?) and his relationship to peculiar experiences brought forth from society, and in understanding this individual's peculiarities which bring forth his happiness, he is able to portray this peculiar aspect of his own nature, that in which is his self, more so than in any other emotional state.