The more I think about these sorts of things, the more I find myself agreeing with Schopenhauer, and with the existentialists to varying degrees — there is no intrinsic "goal" or "meaning" in life. Schopenhauer is generally considered a pessimist, but I see him more like a proto-existentialist. After all, existentialism builds upon the same notion of the meaninglessness of life, except it goes further and examines how one could deal with it.

The problem with adult life, as I wade through it, is that nothing is certain. Unlike physics, where the first principles scale, its hard to know what are the first principles in life.

That's the fun of dealing with human experience versus dealing with hard, observable facts about the world. In the purest sense, the "first principle" of life is that it leads to death. That is, I'd say, the only principle you're going to find. Everything else is subjective experience, and trying to boil it down to any sort of enunciable, universal truth or set of rules is a task doomed to failure.

It seems that happiness is quite elusive

The first snag here would be defining "happiness". In Schopenhauer, happiness is a negative — it exists only as an absence of suffering/pain/struggle. Suffering, on the other hand, is positive. You can only feel "rested" in the absence of exhaustion, "healthy" in the absence of illness, or "safe" in the absence of danger. In this sense, happiness only exists when there is no want. But, being human beings, we tend towards wanting and desiring — a better job, a vacation, a partner, money, food, experiences. And in desiring, we again move from the temporary "happiness" to what Schopenhauer sees as the true state of existence — suffering.

I was reading the bhagavat gita in the hopes that it has some answers to this quandary.

I think the fact that you've turned to a 2,000+ year old text in search of answers to this predicament — and have found the answers unsatisfying — is itself quite revealing about the nature of the predicament itself. It's a question that humanity has been pondering pretty much since we evolved the ability to ponder such things. So far no one has been able to come up with a "good" answer.

Throughout history people have turned to religion, community, entertainment, pleasures of the body and the mind, and all sorts of other things in an effort to craft an answer. If you believe Schopenhauer, all of it is moot, because suffering is the only thing that exists, and we can't escape it while we are alive in this world. He pretty much left it there, which explains why he's considered a pessimist. "Life sucks, and then you die."

The existentialists would encourage you to accept that there are no ultimate answers, much less easy ones, and just do your best to create your own meaning and goals in ways that make sense to you, and allow you to escape the dread of meaninglessness. Looking for sense and meaning outside yourself will only make things more unpleasant.

Of course, this is just one way of looking at the problem. Like I said, no one has found answers to these questions. And I wouldn't blame you if you find this line of thinking rather horrifying. A lot more has been said (and been better expressed) than what I can cram into a comment on HN.

The one suggestion I can offer, at least as a starting point, is to shift your perception inwards. This is something I'm dealing with myself. If you look to the outside world for answers, principles, or examples of how to go about living, you're going to get pulled in all sorts of insane directions. And there's no guarantee that any of those directions lead to satisfaction anyway.