At a general level, the author's answer to the first question is surprisingly obvious: it is difficult to be happy because the universe was simply not built for our happiness. While religions and mythologies have been created to provide some security against this fact, first-hand knowledge cruelly reveals its truth again and again. He says it is best to think about the universe in terms of order and chaos (entropy). That healthy human beings find order pleasing is a clue to its intrinsic value, and to its role in the creation of happiness.

The bringing of order to consciousness, 'control of the mind', is therefore the key to happiness. But what gives us this control? Czikszentmihalyi's research began not by looking at the nature of happiness per se, but by asking the question, 'When are people most happy?' That is, what exactly are we doing when we feel enjoyment or fulfilment? People in a state of 'flow' are those who feel feel they are engaged in a creative unfolding of something larger; athletes call it 'being in the zone', mystics have described as 'ecstasy', and artists 'rapture'.

You and I may recognise our flow experiences as simply those activities (work, a hobby, some kind of service) which seem to make time stand still. The book's best definition of flow comes from the ancient Taoist scholar Chuang Tzu. In a parable, Ting, the esteemed court butcher of Lord Wen-hui, describes his way of working: 'Perception and understanding have come to a stop and spirit moves where it wants.' You stop 'thinking' and just do.

The German philosopher Nietzsche believed that a 'will to power' was the root of human action, but the implication of the flow theory is that a will to order is what feeds this and other motivations. Any activity which creates an ordered sense of self provides us with both a sense of meaning and a degree of happiness.

The formula is simple, but not obvious, and in drawing attention to it Flow is a justifiably celebrated work.