i like this question better, why justify our lives. why indeed? i suppose it is a habit-we have the ability to justify so we feel compelled to do so.
do you feel the need to justify your life? do you feel if you were remembered generations and millenia after your death that would be justification for your life? do you feel something in particular is expected of you?
I think you're spot-on regarding our habit of "justifying" -- our actions, our feelings, our intuitions, and ultimately our lives.
Your question about being remembered generations after one's death as sufficient for "justifying" one's life is an excellent one. Is there really any sufficient answer to the question of what "justifies" one's life, or, referring back to the OP, a sufficient answer about the reason for living, a reason for trying, a "point" to human endeavor? Is there any answer anyone can imagine which would possibly suffice as the "meaning or reason for living"?
Secondly, I wonder even if we could find a personally sufficient answer to these questions, how would it change our present obvious circumstances, responsibilities and actions? Would we cease endeavoring to improve the tragic state of humanity, to lessen the mass suffering in this world we live in, or to lessen the damage we humans increasingly inflict on the very earth that sustains us?
Would we suddenly transform into "great and famous world changers", or would we simply continue as average people, making whatever small difference circumstances allow us for the benefit of "the good", helping others as best we can (even if all we have to offer is a kind word of encouragement, a listening ear, or respect for another's dignity)?
Since I'm at the place where probably 90% of my life is behind me, not before me, I examine my own life's meaning on a smaller, daily basis now. If I've somehow made someone or something or some place a little better, it's been a wonderful, meaningful day!