Some years ago, writing in my diary used to be a usual activity.I would return from school and spend the expected half hour recording the day'sevents, feelings, and impressions in my little blue diary. I did not reallyneed to express my emotions by way of words, but I gained a certainsatisfaction from seeing my experiences forever recorded on paper. After all,isn't accumulating memories a way of preserving the past?

When I was thirteen years old, I went on a long journey on footin a great valley, well equipped with pens, a diary, and a camera. During thetrip, I was busy recording every incident, name and place I came across. I feltproud to be spending my time productively, dutifully preserving for futuregenerations a detailed description of my travels. On my last night there, Iwandered out of my tent, diary in hand. The sky was clear and lit by the glareof the moon, and the walls of the valley looked threatening behind their screenof shadows. I automatically took out my pen...

At that point, I understood that nothing I wrote could evermatch or replace the few seconds I allowed myself to experience the dramaticbeauty of the valley. All I remembered of the previous few days were the dullcharacterizations I had set down in my diary.

Now, I only write in my diary when I need to write down aspecial thought or feeling. I still love to record ideas and quotations thatstrike me in books, or observations that are particularly meaningful. I takepictures, but not very often only of objects I find really beautiful. I'm nolonger blindly satisfied with having something to remember when I grow old. Irealize that life will simply pass me by if I stay behind the camera, busypreserving the present so as to live it in the future.

I don't want to wake up one day and have nothing but a pile ofpictures and notes. Maybe I won't have as many exact representations of peopleand places; maybe I'll forget certain facts, but at least the experiences willalways remain inside me. I don't live to make memories--I just live, and thememories form themselves.

    Grown-ups are often surprised by how well they remember something they learned as children but have never practiced ever since. A man who has not had a chance to go swimming for years can still swim as well as ever when he gets back in the water. He can get on a bicycle after many years and still ride away. He can play catch and hit a ball as well as his son. A mother who has not thought about the words for years can teach her daughter the poem that begins “Twinkle, twinkle, little star” or remember the story of Cinderella or Goldilocks and the Three Bears.

    One explanation is the law of overlearning, which can be stated as follows: Once we have learned something, additional learning trials will help strengthen the related knowledge and skills.

    In childhood we usually continue to practice such skills as swimming, bicycle riding, and playing baseball long after we have learned them. We continue to listen to and remind ourselves of words such as “Twinkle, twinkle, little star” and childhood tales such as Cinderella and Goldilocks. We not only learn but overlearn.

    The multiplication tables (乘法口诀表) are also an exception to the general rule that we forget rather quickly the things that we learn in school, because they are another of the things we overlearn in childhood.

    The law of overlearning explains why cramming for an examination, though it may result in a passing grade, is not a satisfactory way to learn a college course. By cramming, a student may learn the subject well enough to get by on the examination, but he is likely soon to forget almost everything he learned. A little overlearning, on the other hand, is really necessary for one's future development.

    In the early decades of the United States, the agrarian(土地的) movement promoted the farmer as society's hero. In the minds of agrarian thinkers and writers, the farmer was a person on whose well-being the health of the new country depended. The period between the Revolution, which ended in 1783, and the Civil War, which ended in 1865, was the age of the farmer in the United States. Agrarian philosophers, represented most eloquently by Thomas Jefferson, celebrated farmers extravagantly for their supposed centrality in a good society, their political virtue, and their Superior morality. And virtually all policy makers, whether they subscribed to the tenets of the philosophy held by Jefferson or not, recognized agriculture as the key component of the American economy. Consequently, government at all levels worked to encourage farmers as a social group and agriculture as economic enterprise.

    Both the national and state governments developed transportation infrastructure, building canals, roads, bridges, and railroads, deepening harbors, and removing obstructions from navigable streams. The national government imported plant and animal varieties and launched exploring expeditions into prospective farmlands in the West. In addition, government trade policies facilitated the exporting of agricultural products.

    For their part, farmers seemed to meet the social expectations agrarian philosophers had for them, as their broader horizons and greater self-respect, both products of the Revolution, were reflected to some degree in their behavior. Farmers seemed to become more scientific, joining agricultural societies and reading the farm newspapers that sprang up throughout the country. They began using improved implements, tried new crops and pure animal breeds, and became more receptive to modern theories of soil improvement.

    They also responded to inducements by national and state governments. Farmers streamed to the West, filling frontier lands with stunning rapidity. But farmers responded less to the expectations of agrarians and government inducements than to growing market opportunities. European demand for food from the United States seemed insatiable. War, industrialization, and urbanization all kept demand high in Europe. United States cities and industries grew as well; even industries not directly related to farming thrived because of the market, money, and labor that agriculture provided.

    When it comes to medical care, many patients and doctors believe "more is better." But what they do not realize is that overtreatment—too many scans, too many blood tests, too many procedures—may bring harm. Sometimes a test leads you down a path to more and more testing, some of which may be invasive, or to treatment for things that should be left alone.

    Terrence Power, for example, complained that after his wife learned she had Wegener's disease, an uncommon disorder of the immune system, they found it difficult to refuse testing recommended by her doctor. The doctor insisted on office visits every three weeks, even when she was feeling well. He frequently ordered blood tests and X－rays, and repeatedly referred her to specialists for even minor complaints. Even when tests came back negative, more were ordered, and she was hospitalized as prevention when she developed a cold. She had as many as 25 doctor visits during one six－month period. The couple was spending about $30,000 a year for her care.

    After several years of physical suffering and near financial ruin from the medical costs, the couple began questioning the treatment after discussing with other patients in online support groups. "It's a really hard thing to determine when they've crossed the line," Mr. Power said. "You think she's getting the best care in the world, but after a while you start to wonder: What is the purpose?" Mr. Power then spoke with his own primary care doctor, who advised him to find a new specialist to oversee Mrs. Power's care. Under the new doctor's care, the regular testing stopped and Mrs. Power's condition stabilized. Now she sees the doctor only four or five times a year.

    A few years back I worked in a university building that also housed a department full of psychologists, all of whom seemed to see us as perfect guinea pigs(豚鼠) for their latest theories. If an eager graduate student showed up in my office bearing desserts and asked me to pick one, I'd cast a careful glance and ask "Why?" before grabbing the apple pie.

    So one day, when someone from the Psychology Department posted instructions in the bathroom persuading all of us to "Think about five things for which you're grateful every day for a week!" my response was frankly doubtful. I did the math. Five things a day for seven days is a lot of brainpower to expend without so much as the promise of an apple pie.

    I wandered into the office of Heidi Zetzer, the director of our school's Psychological Services Clinic. "What's with the gratitude thing?" I asked. You don't ask an academic question－even a simple one unless you're prepared for a long answer. Heidi came alive, and I sat down. That's when I first heard the term "positive psychology". The gratitude thing, as I had called it, was but one small and simple element of the practice. "Kind of like training the brain to focus on joy," my friend Heidi explained. "It's only a week," she urged. "Try it." I did. And guess what? It worked.

    Every day for a week, I found five distinct things for which I was thankful. They had to be different every day. I couldn't get away with just being grateful for my wonderful husband. But I could, suggested Collie Conoley, another positive psychologist, express my gratitude for specific aspects of a certain person each day. He's a great cook. He always puts our family first.

    Life will never be perfect. I still see new stories that annoy me. The traffic in my city is maddening. I wish I could speed up my recovery. But with just one simple exercise, I'm rediscovering the peace of that old saying: accepting the things I can't change, working without complaint to change what I can, and being wise enough to know the difference.

    And all it took was a little gratitude.