Many people function on a daily basis - whether they consciously express it to themselves or not - on the following principle: "figure out what you want, and figure out how to get it." This may seem like common sense; it may seem like the logical way to approach life. However, it will ultimately lead to a sense of meaninglessness and depression.
A more effective way to view one's existence is to ask: "what do other people want or need, and how can I help them get it?" This is a much more satisfying way to live.