When I was nine years old. I pulled out my grandmother’s dress over my young frame, admiring myself in the mirror. I had no idea what I wanted to be when I grew up. Later in senior high school, I began to dream of being an adult to explore a big world and make adventures. However, I knew adulthood for me was still distant because I supported myself mainly with the money from my family.

Fresh out of college, I was working as a middle school teacher. I was in charge of young people and heavy with that responsibility. I arrived at school early and stayed late, preparing lessons and chatting with students. I was an official adult. I paid my rent and taxes. But I still felt as if I were playing a role. I was the adult authority figure who secretly didn’t feel grown-up in a room full of children. But I wasn’t worried; I was convinced that it would happen soon.

To me, an adult is someone who is mature and trustworthy—a contributing member of the society. We strive to become adults while there is also someone who spends life constantly partying and avoiding responsibility. A grown-up, however, is a state of mind. Our body gets older but something inside us doesn’t feel as if it is progressing as quickly.

In the following ten years, I followed the routines of adulthood: getting married, giving birth and working. My 6-year-old daughter and I often held hands, running breathlessly and laughing wildly. I tried to avoid eye contact with the nearby people who glared at us. I suspect they would prefer adults who would never slide down a giant hill of sand.

I turned 57 recently and it occurred to me that maybe I had it all wrong; I should stop waiting to feel grown-up. What if we embraced (拥抱) the child-like part of ourselves to enjoy it, guilt free? If we’re responsible adults and do all the adult things in a way that works, why should it matter if we don’t feel grown-up deep inside? Non-grown-ups don’t necessarily play games, but it isn’t fun embracing the playful side of life? Why can’t we feel 57 and 15 years old at the same time?

Some time ago, in my class I was about to fail a student for his answer to a physics question when the student claimed he deserved a better score. The examination question sounded “safe”.

“Show how it is possible to determine the height of a tall building with the aid of a barometer（压表）.” The student had answered: “Take the barometer to the top of the building, attach a long rope to it, lower the barometer to the street, and then bring it up, measuring the length of the rope. The length of the rope is the height of the building.”

I argued that a high grade should prove his competence in physics, but the answer did not confirm this. I suggested that the student have another try. Immediately, he worked out his answer: A second best way is to take the barometer to the top of the building. Drop the barometer, timing its fall with a stopwatch. Then, using the formula to calculate the height of the building.

I was shocked by his answer. His method gave me not only a broken barometer but a U-turn in my teaching philosophy. I gave him full marks.

On his leaving my office, I recalled that he suggested there could be a better answer. So I asked him what it was. “Oh, yes,” said the student, “There are many ways. Probably the best,” he said, “is to take the barometer to the basement and ask the superintendent （楼管）. You speak to him as follows: Mr.Superintendent, here I have a fine barometer. If you tell me the height of this building, I will give it to you.

At this point, I asked the student if he really did not know the conventional answer to this question. He admitted that he did, but said that he was fed up with high school instructors’ trying to teach him how to think, and to use the so-called “scientific method”. He just wanted to solve the problem in a practical manner, not just answer the question in an expected way. Hearing this, I really had nothing to do but give the boy a firm handshake, feeling thankful that I hadn’t failed him in the first place and even more thankful, neither had he.