system
A chat on subreddit /r/NoStupidQuestions
human
I think there's also a stress component (or maybe the opportunity to f'up)

You might be physically active in your fast-food job, but you can completely unplug your brain whilst you do them. Simple rules for everything, just need to follow them.  
You might worry about your pay, or the arsehole managing you - but you're never going to be kept awake at night wondering htf you'll manage to get the job done the next day.
gpt
This isn't really accurate in my experience. Yeah each individual task doesn't require much thought but trying to juggle 20 tasks at once and do them as efficiently as possible is very stressful. But also the place I worked was regularly under staffed so I was doing 2 or 3 people's jobs at once.