I have never called in sick during the year I have been working as a Swimming Instructor. I don't do this for the money, because I could easily cover a shift the next week and make up the money. I don't take the day off work because there are never enough instructors, and it's really hard to find cover, especially on short notice. If I take a day off, the kids I teach might have an instructor turn up late, and even if they do get a good instructor covering, that teacher has to spend the first 10 minutes of the lesson getting to know the abilities and confidence of each child. When I take my classes, I know the abilities of each child and can structure a lesson accordingly. Also, when teaching infants and pre-schoolers how to swim, any change to their routine (i.e a different instructor) disturbs and scars them. Spending half an hour crying doesn't help a child swim. Their parents pay a lot of money for swimming lessons, and my job essentially saves lives. So I would rather suffer the sniffles, a headache or even a mild fever for a single day while at work than hinder my students learning how to swim.
(wow, sorry that was so long winded)