Based on your standing in the most recent Winter Olympics, you are the second-best cross-country skier in the world. If you compare yourself with the gold medal winner, your self-esteem will probably , and it may if you compare yourself with everyone else who competed.

decrease; increase        

Explanation:

Self-esteem: In psychology, the term "self-esteem" is described as an individual's complete sense of his or her personal value or self-worth. It refers to the proclivity of a person to like or appreciate oneself. It is often referred to as an individual's personality traits that signify the fact that it is considered as enduring and stable. Therefore, self-esteem is considered as important as it influences an individual's choices and decisions.

In the question above, if the person compares oneself with gold medalist then the person's self-esteem will decrease as he or she is at a lower level and vice-versa.