Taking a sick day is one of the hardest things to do as a teacher. There's a lot of work that goes into it. Preparing for the substitute teacher takes time and effort (that you don't have when you're feeling sick). Then the entire time you are sick you worry that your students will do something horrible to the sub or to your room. So more often then not we choose to just stay and 'tough it out'. Hopefully COVID will change this mindset amongst teacher.