In my "Happy Society" class we started with Aristotle's Nicomachean Ethics, as most studies of happiness do. Aristotle says happiness is the highest end of life, the only end that is not a means to some other end. And happiness is a thing we do more than a condition we have. Happiness is an action of the soul, in accordance with virtue.
In other words, happiness is a project.
Which is why the second book we studied is Gretchen Rubin's The Happiness Project. Rubin read the wisdom and empirical literature of happiness and tried to put it into practice over the course of a year. She, too, started with Aristotle. She was not overtly implementing Aristotle, but the similarity in conclusions is striking.
The puzzling thing for many about Aristotle's argument is that he spend 9/10ths of the book talking about happiness coming from practical virtues, and then in the final chapter says that true happiness comes from contemplation.
Rubin, too, spends nearly all of her project on things that she did to increase her happiness - but the final chapters are about mindfulness, attitude, and reflection. And what she concludes is that what most increased her happiness was not what she did, but what she stopped doing - namely, thinking and saying criticisms of herself and others. A cheerful and contented attitude did more to make her happy than any particular thing she did, even things she did with her children and husband, the loves of her life.
That is, the greatest fruit of Rubin's happiness project came from contemplation of the attempt to act virtuously, more than from the virtuous acts themselves. The virtuous acts were still virtuous, and worth turning into habits, and also happy-making. And I believe that Rubin could not have fruitfully contemplated the attempt to become happy by acting in accordance with virtue if she had not, in fact, wholeheartedly done all that virtuous acting.
But the greatest happiness comes from the contemplation of the action of the soul in accordance with virtue.