Keep going on the right path
Many people know they are doing their jobs well when others are pleased with them. This is because their goal is often to maintain a good image and bring in repeat client/customer business.
However, with some jobs, there will inevitably be people who are unhappy if you are doing your duties well. Take police officers, for instance. When they ticket speeders, pull over drunk drivers or give out parking tickets, they might encounter feedback from very irate citizens who are angry at them for doing their jobs. The same goes for schoolteachers and college professors. If an educator is truly committed to helping students learn, they may pile on a little more homework and force students to push their boundaries more than other instructors. As a result, many students will not like this professional who is merely striving to do their job well.