I got to use NeXTStep at a job for a time and really liked it but it was different enough from my previous experience on mostly System V Unix that it was hard at first and then I switched jobs again and never really played with it again.
It wasn't so much the operating system that was hard for me, but the whole Objective C vs standard C and I wanted to make everything perfect when I should haven't tried to be such a perfectionist. For example I spent way too much time making little things work just exactly the way I thought they should rather than just making it good enough for a user to get their job done.
And for some reason our database was on a Sun Solaris machine and the backup tapes were all unreadable. My predecessor had dutifully backed up the system every night but had done nothing to make sure the tapes were still usable and I guess after a few years of that none of them could be read without errors.
You know you're in trouble when you ask about their disaster recovery plan and they point to a shoebox full of unorganized magnetic tapes in your new office. Just kidding - I was too naive to ask about any disaster recovery plan back then. I just expected at least one tape would work. And I'm not even the one who deleted the thing I was trying to restore - that was my predecessor's mistake.
My boss was paranoid about the idea of someone being able to access our network via dialup and there were NeXTs two with modems, one in my office and another for someone else who needed one for some reason. I "tested" security one night from home. I just wanted to see if failed login attempts would generate any kind of logging for me to notice. I dialed into my co-worker's machine and entered her login (her first name which was the standard there IIRC). Then I entered a password I didn't think could possibly be right (also her first name, the same one I just typed for her username). I don't think I need to explain that no log was generated for a failed login attempt because that was her password.
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I almost forgot to mention this part. Part of that business was basically a media department and they published a magazine specifically for the business who were our clients (mostly landlords). They ran their own little network of Macintoshes and they liked it. I think there were only 4 employees in that department but they were incredibly low maintenance as far as I was concerned. In fact, they didn't need me at all which was good because I was running around trying to do everything else at once.
One time my boss even had me up in the ceiling pulling old cable that was leftover from some ancient computer older than NeXT, I can't even remember what exactly. All I ever saw of that system was leftover cables and a few 8" floppy disks.