It is a question that has been tackled by the wisest of the wise ever since reasoning and awareness came into existence (whenever that might have been).
So, in order to answer this question, which perhaps is unanswerable, we should start with something that everyone wishes they had.
We need not concern ourselves with thoughts of omnipotent beings and their "requirements" or "ways to live" because all in all, these omnipotent beings were most likely fabricated by non-omnipotent beings (ironic).
And so, this makes our task a bit easier.
The question can thus be answered if we take into account only our own thoughts and opinions. Thus, this reason for being here has to be central to all of us. Something which we can all relate to.Â
Wealth? Fame? Advancement of the human race?
Well, not everyone can agree on one concept. Furthermore, all of these concepts all derive from one thing: happiness.
As corny as it may sound, perhaps happiness is the reason we are here. Happiness is something which everyone wishes for. Fame, wealth, and so on; these are all things that a person wishes to acquire because they believe it will lead them to happiness.
From a scientific point of view, happiness contributes to the overall well being of an individual, thereby increasing its fitness (fitness, in this sense, meaning its increased chance to reproduce).
So, when you see things from this perspective, perhaps everything we do stems from the fact that we desire happiness.
But, like the wind, happiness is something that comes and goes.
It is like the tide: outgoing then ingoing.
So perhaps our aim should be to maximize happiness in our lives. Drinking, drugs, lust; these are all things that give us a small and insignificant dose of happiness and in the long run usually contribute to the opposite of happiness. Instead, as the wise have said many times over, our aim should be in finding things that give us an unconditional happiness.
True happiness is something which makes us fall asleep with a smile, looking forward to waking up the next day.
We are all different. For some, this might be finding a cure for a disease. For others, it may be traveling, learning new languages, meeting new people.
Your job in this life is to find that something which gives you this unconditional happiness.
So, challenge EVERY negative thought.
As you progress and start to feel more optimistic you will realize something important. That people can stand against you and try to stop you, but only you and you alone decide what to do with your life. Don't blame others for your weaknesses and your inability to act.
They might try to suppress you, but they can not control you.