Feeling sad is an important part of human nature.

    Jerome Wakefield, a professor at New York University, mentions that feeling down after your heart is broken is normal and may even be beneficial. Recently, Wakefield's students have been coming up to him because their parents are pressuring them to get help for their sadness; often the kids want no part of it. Rather than “listen to medicine,” they want to listen to their hearts. He believes these students' reaction represents an important part of human nature.

    Professor Diener, who has studied happiness for a quarter century, finds that the Scots and many other peoples like being sad, and don't appreciate being told they should be happier. “They say too much happiness might not be such a good thing, no matter where it comes from,” says Diener. He believes it's wrong for the “happiness industry” to send the message that not only can we all be happier, but we have a duty to be so. He argues that what is considered normal sadness is something we shouldn't avoid.

    Eric Wilson, a professor at Wake Forest University, made every effort to smooth out his habitual frown and wear a sunny smile, since a happy expression can lead to happy feelings. He even tried to be enthusiastic. When neither of these made him happy, he concluded that such a happiness movement was no good for him at all. Americans, love for happiness, he writes, creates an environment where sadness is not valued.

    These researchers believe the problem of continuous, extreme happiness should not be surprising, since negative emotions developed for a reason. Fear warns us against the presence of danger, for instance. Sadness, too, seems to be part of our DNA: monkeys, dogs and elephants all display something that looks like sadness. Being “up” all the time can cause you to play down very real threats.

    They believe that only by experiencing sadness can we experience the fullness of the human condition. Their studies show that when you are in a negative frame of mind, you become more logical and more creative. Abraham Lincoln was not limited by his dark moods, and Beethoven composed his later works in a sad state. Vincent van Gogh, Emily Dickinson and other artistic giants saw the world through a glass darkly.

    People who are somewhat unhappy are more motivated to improve both their own lot and the lot of their community. In contrast, people at the top of the happiness charts feel no such urgency. “If you're totally satisfied with your life,” says Diener, “you don't feel like working for change. Be careful when people tell you that you should be happier.”

    Whether it's music, art, stage, screen, restaurant and bar deals, or the great outdoors – there's always something interesting going on in Hong Kong

    Tim Yip: Blue – Art, Costumes and Memory

    What: A well-known visual artist, costume designer, and art director for stage and film (particularly on his work for Crouching Tiger, Hidden Dragon, for which he won an Oscar), Tim Yip has been a proud promoter of Eastern aestheticism(唯美主义)for 30 years. For his first large-scale solo exhibition in Hong Kong, Yip explores the nature of human imagination and the depths of the subconscious mind. Organized by Mark Holborn, the exhibition is expected to be praised due to Yip's vision of “New Orientalism”.

    Where: HKDI Gallery, Hong Kong Design Institute, 3 King Ling Road, Tiu Keng Leng, Tseung Kwan O

    When: Until March 31, 2019

    Alice's Adventure at Starlight Garden

    What: Introduced last year, this exhibition became a huge hit, with more than 6,000 photos and videos posted online every day. Created by 27 multimedia digital artists from Korea, the exhibition features a 30-foot rabbit hole for visitors to explore the fantasy world made famous in the book Alice's Adventures in Wonderland. This Christmas, New Town Plaza delivers a brand-new interactive digital version of the literary work. In particular, check out the seventh floor, with its bright lighting, glittering mirrors and rose-shaped decorations.

    Where: New Town Plaza, 18 Sha Tin Centre Street, Sha Tin

    When: Until January 13, 2019

    We Travel in Our Minds

    What: This exhibition of sculpture aims to present ideas of theatricality, the fantastical, travel and exchange, with figures that take the forms of humans and animals. Made by artist Ethan Murrow, a professor at the School of the Museum of Fine Arts at Tufts University in Boston, these dream-like objects are inspired by puppetry (木偶戏), music, trade, navigation and beyond, with mixed effects of materiality, sound and imagination.

    Where: Duddell's, Level 3, Shanghai Tang Mansion, 1 Duddell Street, Central

When: Until March 10, 2019

    My grandmother often said to me, "You can count the number of your true friends on the fingers of one hand." For a long time I thought this was true. However, I've now discovered my grandmother was only half right. Maybe we do only make a few "best" friends in our lifetime, but those aren't the only people that we can call friends. There are many different types. Let me tell you about a few of them.

    One type of friends is the type I call the "football mom friends". My neighbour Sally is a good example. We both have kids who play football in a football club, and someone has to take them to practise and pick them up. Sally and I and two other mothers do this. We meet sometimes and have tea and talk about what our kids are doing, but those are the only times that we meet each other. I enjoy being with these women, but we don't do anything else together.

    Another type is called the "hobby friend". That's the person you share an interest or a hobby with. Michael and Cater, who are brothers, are a good example of this type. We're all in a bird watching club. Every few weekends the members of the club go on a trip to watch different kinds of birds. There's nothing romantic about my relationship with Michael and Cater, of course. We just share interest in birds.

    Then there's the "other half the couple" type of friends. Jim is married to Rose, a friend that I have known since college. When Rose married Jim, I realized that I would have to be Jim's friend if I want to continue to be Rose's. Jim and I don't share so many interests, but we do have a friendly relationship.

In high school I was very shy, content to hang around with my small group of friends and concentrate on my courses. I was quickly regarded as a "brain". I did so well that by the end of the senior year I had perfect grades and enough credits to give up an entire quarter of coursework.

But in early June of the senior year, the principal called me into his office. He asked me to give a speech at graduation. I gaped(目瞪口呆地凝视) at him, my heart thumping. This was the reward for my hard work? I mumbled something and fled the office, blaming myself for staying away from physics, a subject sure to have ruined my perfect record.

I finally agreed to a compromise. I would share the honour with five other students. And my friend Judy would then give her own, full-length speech.

The graduation day soon arrived. I'd been practising my speech for days, and I had it memorised. The first half hour of the ceremony passed in a blur, and then my moment came. My name was announced. I managed to reach the platform without falling down. I faced my classmates. My voice trembled a little, but mostly it was clear and strong. But within seconds, I was done and headed back to my seat. I accomplished something I'd never dreamed of—I spoke in front of hundreds of people.

Although I didn't realise it at the time, the successful completion of that speech gave me the confidence to participate in class at college, to give verbal reports, and to eventually break free from my shyness. I would never have chosen to give a speech at graduation ever. But I'm glad I did. I no longer hesitate when I'm faced with the prospect of doing something I dread. I know it may very well turn out to be one of my shining moments.

Robots have long been drawing inspiration from animals, with the creation of robot dogs or snake-shaped robots. And yet, the field of robotics is far less enthusiastic about the other kind of living things—plants. Barbara Mazzolai, an Italian roboticist owes this to a misconception about plant behavior: that they cannot move or think. "It's not true at all," she says. To challenge this view, Dr Mazzolai and her team recently launched a machine called "FiloBot", a robot based on a climbing species.

To survive, a climbing plant must switch between several different behaviors. In forest environments, it must first grow out of the soil and travel along the ground in search of a support to hold onto, such as a nearby tree. Once a support is located, though, the plant fixes itself around the object and then growing towards the light. To choose the best angle to grow upwards, a climbing plant uses its shoots(芽) to receive information about light and gravity.

FiloBot has sensors on its main shoot. It can 3D-print its body with plastic and grow at a controllable rate. These functions researchers found, enabled FiloBot to cross gaps, and find things to attach to. The lack of heavy on-board computing device means that it is light and requires minimal care, while its slow pace means that it doesn't disturb things around it, making it possible to move through a complex, unseen environment, or monitoring disaster sites.

For now, FiloBot is still being tested. Its tendrils(卷须) have not left the laboratory. Still, it has already been employed in deconstructing plant behaviour. For example, it was long assumed that climbing plants find their supports by growing towards shade, though the exact mechanism was unclear. FiloBot could imitate this behaviour by detecting far-red light, which is typical of shaded areas, providing clues to how plants do it.

Dr Mazzolai hopes that such projects will inspire other roboticists to take their cues from plants and develop completely new technologies.