Why would someone who is happy with the job not perform at a higher level than the disgruntled worker?

A happy employee may focus on job satisfaction and maintaining a positive work environment rather than pushing for higher performance. They might prioritize collaboration and team dynamics over individual achievements, leading to a more balanced but less competitive approach. In contrast, a disgruntled worker, motivated by frustration or a desire for change, might channel their energy into higher performance as a means of expressing dissatisfaction or seeking recognition. Ultimately, differing motivations and priorities can result in varying performance levels, regardless of overall job satisfaction.