I only get sick during vacation. Like all decent teachers should
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I never taught music, but I have taught other subjects, and I was very lucky indeed. I always got sick on my days off. I missed very few classes in my entire teaching career. I think there's truly something to be said for a job that you genuinely love.

I don't think I ever had a bad day teaching. Of course, I always taught college students who were eager to learn. I have no idea what it might be like trying to teach high-school students who don't even want to be there. I don't think I'd be interested in even trying to do that.
Although, I would think that teaching piano students would in general be students who are interested in the subject at hand. I mean that would be better than trying to shove something like English down the throats of students who don't want to learn it.
I was lucky, I taught math, physics, and other technologies, and the students were always eager to learn.