Generally the extent of demotivation is proportional to the perceived disparity with other people or inequity, but for some people just the smallest indication of negative disparity between their situation and other people's is enough to cause massive disappointment and a feeling of considerable injustice, resulting in demotivation, or worse, open hostility.
Some people reduce effort and application and become inwardly disgruntled, or outwardly difficult, recalcitrant or even disruptive. Other people seek to improve the outputs by making claims or demands for more reward, or seeking an alternative job.