Jill, now 40 years old, used to run 5 miles a week in her 30…

Jill, now 40 years old, used to run 5 miles a week in her 30’s. As running that distance became more challenging, she adjusted her routine to 2 miles a week. Despite this change, Jill maintains a positive outlook and high self-esteem. What psychological concept best describes Jill’s approach to her fitness goals?