As a boss, I always stress out a bit when someone calls in sick, because I have to scramble to make sure their shifts are covered, but I really don't want them to be here when they aren't feeling well. I'd rather have just one employee out sick, than all of my employees out sick.
Unfortunately, I don't always have the luxury of calling in sick. In fact, I'm sick right now and have been for the past few days. I took half a day off yesterday, but I'm here today. The reason: If I don't come in, the library can't open. I would much rather be at home in bed, but I don't have a choice. I'm sure I won't be feeling better tomorrow, but I have a class that I must attend and can't reschedule, so I'll be there for that, too. I'm really not impressed by people who can take a day off when they are sick and choose not to.