Two groups of graduate students were given rats and instruct…

Two groups of graduate students were given rats and instructed to teach the rats how to run mazes. Group 1 was told that they had “very smart” rats that should learn quickly. Group 2 was told that they had “very stupid” rats that should learn slowly. In actuality, neither group was any different, and the rats were randomly assigned. In spite of that, when the experiment concluded, the rats taught by Group 1 had learned the maze much more quickly. How can that be explained?