What makes our lives meaningful is that we find the activities we engage in to be worthwhile. Our determination to carry out projects we have created for ourselves gives our lives meaning. We feel that life is meaningless when most of our desires which we regard as important are frustrated. Whether we regard life as meaningful or meaningless depends on the degree to which our important desires are frustrated.
...first, it is necessary to say something about the problematic phrase, 'the meaning of life.' What is it supposed to mean? As a rough first attempt, we might say that a life is (or is not) meaningful if it is worth living. But worthwhile for, or to, whom? Is worth a matter of subjective appreciation, of being valued, by some person or persons? Or might the question whether a life is worthwhile have an objective answer, quite apart from what anyone thinks about the matter?