When I was a small boy, I noticed that though many of the adults around me were wealthy and educated, they were not always happy and this sometimes led them to behave in ways, which I, as a child, thought strange. As a result of that, I decided to try to understand what happiness was and how best to achieve it. It was not surprising, then, that I decided to study psychology. On arrival at the university, I was disappointed to find that academic psychologists were trying to understand human behaviour by studying rats in a lab. I felt that there must be other more useful ways of learning how we think and feel. I decided to build my career on trying to discover what made others happy. I started out by studying creative people such as musicians, artists and athletes because they were people who devoted their lives to doing what they wanted to do, rather than things that just brought them financial rewards. Later, I expanded the study by inventing a system called “the experience sampling method”. Ordinary people were asked to keep an electronic pager ( 传呼机 ) for a week which gave out a beeping sound eight times a day. Every time it did so, they wrote down where they were, what they were doing, how they felt and how much they were concentrating. This system has now been used on more than 10,000 people, and the answers are consistent: as with creative people, ordinary people are happiest when concentrating hard. I found that the most obvious cause of happiness is intense concentration. This must be the main reason why activities such as music, art, literature, sports and other forms of leisure have survived. In order to concentrate, whether you're reading a poem or building a sandcastle, what you need is a challenge that matches your ability. The way to remain continually happy, therefore, is to keep finding new opportunities to improve your skills. This may mean learning to do your job better or faster, or doing other more difficult jobs. As you grow older, you have to find new challenges which are more appropriate to your age.