I'm one of the people who never calls in sick. The last time I did, it was for pneumonia and I couldn't walk.
This isn't because of a false sense of feeling indispensable, it's a fact. Back in my days working in a "Dilbert cube", this wasn't the case. Since being a victim of a workforce reduction and having to resort to my plan B, it is. I'm responsible for keeping my customer's equipment fully functional, even when I'm not. The next closest guy is over 100 miles away, and has his own problems.
Competition dictates that I either keep the customer happy, or they switch companies. If that happens often enough, I become unemployed. Been there, done that, ain't interested in repeating the experience. I am conscientious enough to warn folks in the immediate area to keep their distance, though. It seems to be appreciated, and they are not only happy to see me, but ecstatic about the situation. A down machine means lost revenue. In these times, that's bad news for both of us.