Whenever the phrase "graveyard shift" or "working graveyard" was used when I was a kid, I always assumed it entailed working outside at night, maybe not necessarily in a real graveyard, but any sort of creepy environment with a lot of digging. I think it stems from growing up in a mining town and picturing a bunch of guys somberly digging for ore and stuff with shovels in the middle of the night. I wasn't very swift as you can probably tell.
A childhood belief about work

others believed things like this
- i used to believe the graveyard shift was when you worked in a graveyardAnon
- I used to think that the graveyard shift was men that dug graves at night.— bianca w.
- i used to think that the "graveyard shift" meant that they actually had to go out and dig graves. Anon
- I used to believe that when you visited a graveyard, the ground would suck you in and that is how you died.— Megan
- I used to believe that if you spoke while driving past a graveyard that Frankenstein would come after you.— Sabrina R
- I used to believe a dead end sign meant there was a graveyard at the end of the street or zombies — Still Out There