Experimenters simulated a non zero-sum game, when the performance of one student would not impact the performance of another.
Though an unlimited number of high grades were available, students sill perceived that a high grade achieved by one student would result in a lower grade for the other.
Even when there are unlimited resources, people tend to perceive situations as zero-sum, where one person’s win is another’s loss.
See the full study here :
Meegan, D. V. (2010). Zero-sum bias: Perceived competition despite unlimited resources. Frontiers in psychology, 1, 191, https://doi.org/10.3389/fpsyg.2010.00191