I’ll intellectually/emotionally/physically hard as answers. For me its either 12 hours straight “punching tubes” on a very large scotch marine firetube boiler at the beginning of my career or Easter around a decade ago when I was working with troubled teens and had to engage in 5 separate protective holds in one 16 hour double shift. The former was all physical and the latter was a combination of emotional and physical.
Watching overpaid engineers not understand basic concepts or struggle to do things like check voltage with a multimeter.
Watching horribly sloppy safety procedures.
Interacting with safety auditors who don’t know how their own equipment works and insist on useless safety measures or fail to insist on proper ones.
Being blamed for a problem outside my control even after identifying exactly where the problem is coming from and who they need to call to fix it. (Then having to repeatedly explain this to increasingly higher levels of management who are increasingly detached from the details.)