I think if you decide that any book is about Only One Thing you're probably wrong. Even if that thing is in there.
To the European, it is a characteristic of the American culture that, again and again, one is commanded and ordered to 'be happy.' But happiness cannot be pursued; it must ensue. One must have a reason to 'be happy.' Once the reason is found, however, one becomes happy automatically. As we see, a human being is not one in pursuit of happiness but rather in search of a reason to become happy, last but not least, through actualizing the potential meaning inherent and dormant in a given situation.