The book itself has a great quote about this:
You've got to be hurt and upset; otherwise you can't think of the really good, penetrating X-rayish phrases. (Ch. 12)
Being able to experience the full range of human emotions, being able to try and to fail... these are the things that promote understanding and that lead to invention. When people are complacent - like the people in the book - than they are ignorant. They do not seek out new ways of doing things. They do not try to create and to be different. They just exist. This is, of course, is what Huxley is showing us through his dystopia.
Our world is not the same as Othello's world. You can't make flivvers without steel-and you can't make tragedies without social instability. The world's stable now. People are happy; they get what they want, and they never want what they can't get. (Ch. 16)
This world that is described may sound appealing, but as we see, it leads to a lack of individuality, a lack of meaningful connections. Who wants to live in a world without tragedy? Tragedy is what reminds us that we are human, and it is what makes comedy so special.
Actual happiness always looks pretty squalid in comparison with the over-compensations for misery. And, of course, stability isn't nearly so spectacular as instability. And being contented has none of the glamour of a good fight against misfortune, none of the picturesqueness of a struggle with temptation, or a fatal overthrow by passion or doubt. Happiness is never grand. (Ch. 16)
Huxley encourages us to believe that misery is as important, if not more important, than happiness in our experience as humans. It leads us to grow, to improve, and most of all, to feel in a way that nothing else can.