And if we do obtain something that makes us truly happy- a relationship, a dream home, a career triumph- the happiness quickly fades, thanks to the mechanism known as the 'hedonic treadmill'. We adjust to new circumstances so well that new sources of pleasure soon become part of the unnoticed backdrop of our lives. From an evolutionary standpoint, at least, it makes perfect sense that we're permanently dissatisfied. A creature who could obtain long-term psychological satisfaction from a single hearty meal, or a single episode of sex, wouldn't fare well at spreading genes.

But the most frustration complication with happiness, surely, is the self-defeating truth that focusing on achieving it makes it harder, perhaps even impossible, to obtain. "Ask yourself whether you are happy and you cease to be so," wrote John Stuart Mill, and researchers have since demonstrated that people who value happiness are in fact less likely to experience it. True happiness arrives unpredictably- and its usually only after the event that you realise it paid a visit.

Oliver Burkeman