Happiness has been a puzzle to me for about 60 years, ever since 1944, when Europe was coming apart at the seams. My father was a consul in Italy and my mother, sister and I had gone to live with my grandparents in Budapest. I was ten years old and I watched with astonishment as relatives and friends who were wealthy, educated and well-connected suddenly turned into scared refugees in a land turned topsy-turvy. Walking out of the house could get you a stray bullet from the Nazi invaders, or from one of the Allied fighter-bombers cruising above. And each day the Soviet armies were pulling closer. In this mindless milieu, it seemed obvious to ask: “Why can’t seemingly sane adults live happily?” My trust in grown-ups, in the wisdom of culture, tradition and authority, suffered a severe blow. No longer able to take “normal” life for granted, I resolved to understand what happiness was and how best to achieve it.

During the subsequent teenage years of searching, all the obvious answers fell short. Religion and philosophy were too dogmatic — after all, they had not helped to prevent the war. Literature and the arts seemed mere palliatives to the otherwise wretched human condition. Then, in my late teens, I stumbled upon the teachings of Carl Jung, a man whose psychology confronted human frailty head-on. Unlike adult institutions such as the Church or school, this was not hypocritical, neither was it dogmatic. Like science, it seemed open to growth and improvement.

No surprise, then, that I decided to study psychology. But on arrival at the University of Chicago 50 years ago, I was dismayed to find that academic psychologists were trying to understand human behaviour from what they learned from rats in the lab. Inadvertently, my vocation had been called. Having decided to try to achieve personal happiness, I became more ambitious. I resolved to build my career on trying to discover what made others happy also. Initially, I studied people whose lives appeared to be free and creative — musicians, artists and athletes. Here were people who devoted their lives to doing things they liked, rather than things that reaped external rewards. I expanded the study by inventing a system called “experience sampling method”. A random sample of people were asked to keep an electronic pager for a week which was programmed to beep eight times a day at random times. Every time it did so, they wrote down where they were, what they were doing and with whom — and filled out a numerical scale charting how they felt, how much they were concentrating, etc. This system has now been used on more than 10,000 people and the answers are consistent: as with those living creative lives, they were happiest when in a state of concentration.

Thirty years of research and 18 books later, I have proved that enduring happiness is quite different from what most people think it is. It is not something that happens. It is not something that can be bought or hoarded. These conclusions have been confirmed over the years by those social scientists brave enough to venture into the uncharted waters of happiness research. Their surveys showed that wealth and comfort are not sufficient conditions for a happy life. Nations where the per capita GNP is less than £10,000 are generally lower in happiness than nations above that threshold. This suggests that a minimum of material comfort is necessary.

But below and above that dividing line, the way people assess their happiness has very little to do with how much poorer or richer they are. Multi-millionaires report being only infinitesimally happier than their poorer fellows, while people living in poverty are often quite happy. Over the years, I came up with the expression “flow”: a term to describe the common denominator among those people who deemed themselves happy. The most obvious component of happiness, I found out, is intense concentration, which is the main reason that activities such as music, art, literature, sports and other forms of leisure have survived. The essential ingredient for concentration — whether it happens when reading a poem or building a sand castle — is that it involves a challenge that matches one’s ability. The only solution to achieve enduring happiness, therefore, is to keep finding new opportunities to refine one’s skills: do one’s job better or faster, or expand the tasks that comprise it; find a new set of challenges more appropriate to your stage of life.

Paradoxically, the feeling of happiness is only realised after the event. To acknowledge it at the time would only serve as distraction — the rock climber would lose his footing, the chess player his game. Out of all the moments pinpointed by people I have interviewed, their best are with hindsight. Just as a smell might evoke a memory, happiness is realised in its aftermath. As I look back at a life devoted to happiness, I often wonder whether I have achieved it. Overall, I think I have and my belief that I held the keys to its secret has helped immeasurably.

Ironically, my unhappiest moment was when I achieved what most would consider success. When my book Flow: The Classic Work On How To Achieve Happiness took off, I had to fight complacency and reclaim serenity. As I get older, I find myself reinventing challenges. I gave a lecture to businessmen during the recession of the 1990s. What affected them most, they said, was an inability to nurture the young talent they believed would be their legacy. When I asked Dr Jonas E. Salk, the inventor of the polio vaccine, his main aim in life, he answered “to become a good ancestor”. The ultimate challenge, perhaps, and one to which, in old age, I rise willingly.