There's an interesting piece in the Guardian here about how pressure to be happy all the time contributes to making us unhappy. (Hat-tip: Lee Jones.)
All very sensible, but not anything particularly new. It's something that J. S. Mill was well aware of as demonstrated by this passage (from chapter 2 of Utilitarianism, shortly after the higher pleasures bit):
"If by happiness be meant a continuity of highly pleasurable excitement, it is evident enough that this is impossible. A state of exalted pleasure lasts only moments, or in some cases, and with some intermissions, hours or days, and is the occasional brilliant flash of enjoyment, not its permanent and steady flame. Of this the philosophers who have taught that happiness is the end of life were as fully aware as those who taunt them. The happiness which they meant was not a life of rapture; but moments of such, in an existence made up of few and transitory pains, many and various pleasures, with a decided predominance of the active over the passive, and having as the foundation of the whole, not to expect more from life than it is capable of bestowing. A life thus composed, to those who have been fortunate enough to obtain it, has always appeared worthy of the name of happiness. And such an existence is even now the lot of many, during some considerable portion of their lives."