"There is no mystery to happiness.
Unhappy men are all alike. Some wound they suffered long ago, some wish denied, some blow to pride, some kindling spark of love put out by scorn - or worse, indifference - cleaves to them, or they to it, and so they live each day within a shroud of yesterdays. The happy man does not look back. He doesn't look ahead. He lives in the present.
But there's the rub. The present can never deliver one thing: meaning. The ways of happiness and meaning are not the same. To find happiness, a man need only live in the moment; he need only live for the moment. But if he wants meaning - the meaning of his dreams, his secrets, his life - a man must reinhabit his past, however dark, and live for the future, however uncertain. Thus nature dangles happiness and meaning before us all, insisitng only that we choose between them."
From Jed Rubenfeld's The Interpretation of Murder.