I normally don't like "Happiness" books, perhaps because they are often too removed from the heavy stressors and pains that people can face and being "happy" doesn't seem to be the final point or the most fulfilling. This book does try to acknowledge that.
I wondered if a better goal is "harmony", meaning learning to accept, flow, either avoiding or enjoying or improving to bring greater harmony within ourselves, between ourselves and others, and in taking the sweet and sometimes bashing music of life and trying to make a sort of harmony out of it, that we offer back to life.
The below site has another contrasting viewpoint on "happiness" too
"Happiness is not the purpose of life"