Well that's the point of philosophy, isn't it? To figure out what we're supposed to do. For some people, just living life going through the motions is enough, and they never stop and ask this question. Other people keep bouncing from philosophy to philosophy, or religion to religion, looking for something that fits. Some of those people find something that works, and stick with it. And of course others just kill themselves because they never can figure out an answer that satisfies them, so life seems infinitely meaningless and they see no reason to keep going.