I'll probably get death threats for saying this, but:
If you know the subject (especially if it's a hard science), there isn't much new stuff to learn in order to excel at your work. Conversely this is the hardest part about most jobs -- staying relevant.
Then add a lesson plan routine and you barely have to think.
To top it all off you work 8-9 months / year, get all the major holidays off at no expense, and are entitled to regular wages based on seniority, degrees, and additional certifications.