Due to your high level of motivation and repeat successes you are get selected by superiors to do more work than your peers because you do your job and good at it. This frequently entails extra hours, multitasking, et cetera. The punishment is that you get to watch the underperformer, who is not doing their job, get rewarded via time off, free time, leave work on time and so on. This is common in the military and other government jobs where, due to bureaucracy, it is difficult to get rid of a bad employee.
Sean isn't a workaholic or a brown nose. Since his work associate Steve does nothing all day long, Sean's performance punishment is that he always has to stay late and take on extra projects to make up for Steve.