Mental and emotional fatigue accrue and exhibit themselves differently sometimes, but often matter quite a bit in the end. Plenty of people choose to leave well paid office jobs for more physical jobs that pay less. Unless you think they have a mental illness or are stupid, presumably they did it for a good reason.
He charged much less than I earned in the same two days configuring AWS lambda functions. It's hard to imagine I had the more exhausting job.
Teaching is just sooooo exhausting.
They can tinker with mechanical things for a 12 hour crunch session before a robotics competition, and end up achy, hangry, and physically tired. But it might not be as exhausting as as an intense 1.5 hour math class or chasing a bug staring at screens for a couple of hours.