Who served you your food today? If you ate any of the campus dining halls, you were very likely served by a fellow student.
Serving food and cleaning up in the dining halls is one of the most visible student employment opportunities on campus. It makes sense why a lot of students would try and pursue part-time or full-time work on-campus. Working on campus provides them with a fairly convenient place to earn some cash and it fills the gaps between classes.
However, the downside of this is that students who work on campus have to stay, well, on campus. We imagine that if you had to work at the Rec Center or a dining hall all the time, you would develop a general dislike for those areas of campus. On top of this, a lot of these jobs can be pretty thankless. Painting lines on the Intramural Fields, serving food to fellow students, or helping out in the library, are jobs that are expected at a university.
Not to imply that the whole of the student body treats their fellows badly, but we do occasionally take them for granted.
So, when you can, let them know that you appreciate what they do because at the end of the day, they are students too.