Mary never liked math and did poorly. When she decided to think of it as a fun challenge, her performance improved. This is an example of a change in:

I believe the answer is: perception

Perception refers to the angle that people choose to observe their situation. Difference in pereception could affect success rate since it could very much related to the viewer's self-esteem. Those who always see themsevles as inferior tend to find excuse to not making an effort to address their problems.