Aside from punched card stuff. I started life in TOPS-10. 78 vintage, not very heavily modified locally as I recall. (people did run local mods, I don't think we'd applied any)

I had forgotten TOPS-10 had a logical equivalent of a mount point, the MFD. And I had forgotten inside the [xxx,yyy] group/user identity directory, you could nest 5 sub-directories deep.

5! such humongous nesting! who could need more than 5 levels deep!

What I did remember is there was no evident ".." equivalent in the commands to "be" in a directory. The idea of needing to go back to your parent, positionally inside a subdirectory but without recourse to the actual path down from the MFD appeared to be missing. I suspect whoever designed this was living their best life in JCL and saw no interaction on paths as needing "optimisations" = SET DIRECTORY obviously demanded a path down from an MFD. Fool of a took!

By the time of VMS, you had the same $MFD:[path.path.path...] structure but now up to 255 nesting levels deep, and the "-" nonce directory meant "the parent to the one you are talking about" so at least in hypothesis a "cd .." command was possible without needing to know the descent path. 255! magic numbers! Who could need so many nesting levels?

When I got the great uplift to Unix in 82 and realized . and .. existed, It was a very strong mind-officially-blown moment. Its like the zen koan for the ages: Who the hell thought it was ok to design a filesystem ANY OTHER WAY. I simply cannot handle that I was using some system (Norsk Data?) around the same time and it didn't have cd .. -It still had a TOPS-10 class view of the world as a descent tree only. Stone Age!

I still regret that the newcastle connections ... naming model didn't get up. I think it was very nice.