It's a very different job from what most people think. Because we all went to school as kids, have our own experiences, maybe saw some things that wouldn't be allowed to happen today, but mostly had experts who'd practised making it look easy, people think it's easy.
It's full on and inflexible. It's not the long hours and working at home that take it out of you, it's the intensity of being in the classroom for five or six lessons back to back and giving it your all, providing exactly what 30 different people need at once, anticipating misconceptions and changing what you planned, answering questions, and making thousands of decisions to manage behaviour and ensure everyone learns. Then, all you've done is generate work for after the work day should finish: marking, data drops, behaviour logs, reports, reading.... Then you have to work to plan what's happening the next day before you can get there. If you're ill, this needs to be redone because your plans won't work without you, and you have to change for a non specialist before you can actually look after yourself.
You work so you have work to do at work, then work on the work from work.
Amongst this, parents might question a perfectly reasonable choice you made because their child didn't like it, or tell you to run a detention for their child's bad behaviour during your unpaid lunchtime to suit them, SMT might walk in while you're sitting down for a second and criticise you, you don't have time to have a drink or go to the loo if anything happens to take up your break or a child or colleague needs help, because that's the only time you're not in a lesson, the general public thinks you go home at 3 as well as never being more than a couple of months from a week off, which is the only time you can ever ring the doctors when they're open.