As storytellers we impart meaning to our lives through stories. The stories of our lives, or families, our nation, those we admire, those we detest, our gods if we are believers, etc. In the back of our minds we recognize that we are mere motes of dust in the world "in itself" but we can’t bear it, so through our stories we impart our meaning and become human. This is the point Sartre was trying to make if I understand him correctly. We are responsible for whatever meaning our lives have.