Happiness in this novel is depicted as an appreciation of the intellectual challenge of reading, absorbing, and thinking about humanity's great books with the intention of using this accumulated wisdom to build a better world. This version of happiness emerges gradually through the consciousness of Montag. He comes to increasingly question his society's shallow definition of happiness when events in his life collide with and contradict what his culture tells him is true.
In his world, happiness is seen as the superficial, mindless pursuit of pleasure. As Beatty explains it, reflecting the orthodox viewpoint of his society, happiness comes when people are all the same. Standing out, being different, and asking too many why questions all lead to trouble and dissatisfaction. The smart kid is the one who is bullied and tormented. Therefore, the society has engineered itself so that nobody has to think or worry about big questions or the big picture. People can simply immerse themselves, when they are not working, in having a good time.
Events in Montag's life call this version of happiness into question. Talking to Clarisse shows Montag how seldom he has a real conversation with anyone or notices the natural world. Mildred's attempted suicide reveals that her life of shallow pleasure has left her empty and desperate. When a woman whose books the firemen are burning kills herself rather than live without reading, Montag begins to wonder what he might be missing. Montag is also troubled by all the people in his culture so bored and dissatisfied that they turn to violence.
All of this leads Montag to the forbidden act of reading, and from there, to life as a renegade. He becomes an enemy of his society, until, soon after this, his culture blows itself up, leaving Montag and other book loving survivors to try to build a better world.