i have thought about these things a lot in the past. i read a lot of philosophy, psychology, about religions... it was my therapy during my depression. i never went to a therapist. well, actually i did once, but true to form i told her that nothing was wrong, lol. so that was my first and only session. i also never took drugs.
anyway... i found that the basic principles in buddhism made the most sense to me... by that i mean balance. i don't think it's useful to me to ask why too much. it is useful to analyze and learn, though, but i found myself thinking in circles, if i pursued that route too deep.
Ti is really my guide. Fi and Ne are the ones giving me peace, but that's enough for me. for me to be happy i don't need to ask why all the time. my Ti is telling me "it is what it is". so i go about around the probable facts. for me it's very important to keep myself "separate" enough to be able to be objective with myself and balance my actions.
when my thoughts are in balance with my actions, i'm usually happy... or simply... you need something to do, something to love and something to wish for...
a positive attitude is also important to me, but to me that means acceptance, as well. in order to reach some of my goals i also need to accept that i will never know "the truth"... and in fact, i think that's irrelevant. i don't think it's our "business" to know some spiritual truth. for me it's enough that i feel that there (probably) is more to life than what we are able to grasp (at this point). that thought gives me "the value of life".
for me happiness is about the pursuit of making the best of things. i don't pursue to be "perfect", but i pursue to live. there is no other reason for me to live than life itself.