How Do People Go to Work When They're Sick?

I know people (like my father) who have had the flu and still manage to go to work. When I have the flu I can barely stand. How do people manage to go to work when they're sick? How do they get motivated? I wish I could be like them, I hate the useless feeling when I am sick.

Suggestion:

for some its money. for others lik myself, i cant survive without working. i get one day a week off and its horribl idk wat to do. i sliced my finger open one day and had to put a glove on then tape ovr it so my boss wudnt send me home. i went to an urgent care aftr work n got 7 stichs workd the next day. work is all some can do