An Incentive Problem I was always thinking of writing at the right time – when I finish my work at school and have enough leisure to sit down. However, I found it not so realistic: it only ended up not writing anything! And my inspirations for many interesting topics faded away. So I decide to write small pieces when I feel like it. This time, the story is about my teaching assistant (TA) experience for an international class. This class is a little bit special, because most students are government officials coming from the developing or the least developed countries. Studying in China for master’s or PhD degrees, they are eager to bring back home Chinese development experience. I am working as a TA for the international trade class, responsible for distributing printed slides, announcing important notices and solving problems when necessary. Teaching international trade can involve a lot of modelling. But many students do not have solid mathematics or economics background. So in the first Ricardian model class, students started to complain. Some of those who have no background, without previewing the slides even when recommended to do so, interrupted the professor many times for very basic questions, while those who have background, usually remained silent at the back. The diversity of the class has added to the difficulty of teaching and meeting everyone’s need. An angry student came to me and said, “I think you should not provide printed slides for the class.” I usually provided printed slides for all students, but I did not realize its connection with this issue. So I asked him why. “It is wasting resources and also making students lazier. Because if you print it out for them, they will only preview it when they come to the classroom and get the slides. But if you let them print for themselves, they are more motivated to learn because it is not a free lunch.” Alas! there may exist an incentive problem behind this seemingly trivial move. Providing free lunch or not can impact how people behave. It has already been discussed in some economics literature, such as whether mosquito nets should be provided for free in disease-stricken areas. Although reluctant to admit he might be right, I took his advice and informed students that printed slides wouldn’t be available next time. Of course, I did not tell them that it was for motivating them to learn. But instead, it was for the sake of “protecting our environment”.