You are right about those two things, but on a side note, we people still do those things. Also, your question can be rephrased as:

What do we absolutely know to be the reason of existing here?

The very question we humans have asked since day one and as you said no one has a definite answer for it or maybe no one ever will. And maybe that's the beauty of it, a mystery that can't be solved but still, it has to be solved. Some people give an answer to this question from their religion but then there are so many of them who has it right? Or maybe nobody has it right.