The math teacher is too tired.
It's not easy to do any job now. Generally speaking, being a teacher is good, at least it is stable and not too intense. You say you have four math classes a day, but if you go to work, you have to work 12 hours, which means eight hours plus three or four hours of voluntary overtime. Working in an enterprise is more tiring now. Foxconn engineers have jumped more than a dozen times and don't know what they do.