I had been working for a peach of a boss for 10 years; he treated me with respect, he thought I had a brain in my head, and he was a fun guy to talk to.
Then the company decided to sell, and my job was going to be cut (along with my boss's, naturally). So I looked around and found one in another part of the company. It was in a specialty I hadn't worked in before, and I thought with the training I would get, this would look good on my resume.
Since this is Bosses From Hell, you know this isn't going to turn out well.
I knew that this particular boss had gone through several assistants in just a couple of years; but I had dealt with (what I had thought) was a difficult boss before, and I handled him pretty well. The problem this time around was that this boss was used to having a lot of assistants to help file things online, and most of them were split off into another group.
It was just me, along with a temp.
After suffering a major illness that kept me out of the job for about a month, I came back. Not so bad, so far. But when was I going to be trained? There was supposed to be an intensive 2-day training in Washington, DC that I was supposed to take, but it kept being put off, and being put off...
Due to several different factors, I didn't take the hint to get the hell out of there. And when we moved to a different building, the entire experience went into the toilet and never recovered.
Without the training, it was up to the temp to teach me what to do. Not fair to her or me, but my boss in essence said, "Live with it." Now, again, this was specialized stuff, and I dutifully took down everything the temp told me. Everything. Made a nice manual, which I always referred to.
Were there some errors? Yes, I'll admit that. But they weren't going to lose money because of those errors. My boss saw it another way, deriding me for the littlest things ("No, it should be this!"), making me feel like an idiot.
To say my confidence was shattered was putting it mildly. She put me down every step of the way, even though the temp told me that what I was doing was the work of 3 people! We were making do with 2. Eventually, I was fired from that job, not because I wasn't trying but because my boss thought it was only a matter of time that I'd make a mistake and cost the company a lot of money.
I tortured myself in this job for a little over a year, crying on the way, crying on the way home, wondering what the next thing I did wrong she would find and tell me about over and over.
Lesson learned: If a manager has been through several assistants in a short amount of time, do NOT take the job. It's a red flag that the manager is too demanding, too demeaning (to the assistant), or both.