Promoting technical people with no management experience into management jobs, without providing them with any training or guidance. (Happened to me.) Writing code and managing people require very different sets of skills, and just because you're good at the former doesn't necessarily mean you'll be any good at the latter (or that you'll enjoy doing it).
(Similar problems can happen when a bunch of people with no management skills decide to found a company and start hiring people.)
Yes, this. I'd add that you end up losing a probably (as he/she's been promoted) skilled engineer as well. Promotion via management is what forces people who might not have the "people-skills" to accept management jobs because they want to be valued.
This reminds me of an article from Rands in Repose:
As I wrote about in Being Geek, the Curse of the Silicon Valley is that great engineers are often promoted to leadership for their hard work. While many succeed in this role, an equal part fails because the skills required to lead are vastly different than the ones required to be an engineer. The Curse is that we’re often placing our most valuable engineers in a role where they’re predisposed to fail.
Think of it like this: there’s a large population of immensely talented engineers that should not be leaders. There is no amount of training that would make up for the talent we’d extinguish by teaching them how to write annual reviews.
But everyone wants to grow.
Unfortunately, in many companies the only perceived growth path is via management.
I read lots of books about management, I tried to emulate what managers who I thought were competent were doing, and I made lots of mistakes and tried to learn from them.
There were some mistakes that I was never able to recover from, like being too friendly with the people who reported to me - that makes you really dread the prospect of having to lay someone off, makes it hard to give difficult feedback, etc.
Eventually, after being a manager for several years, I decided to go back to being a developer, and now I'm much happier.
(Similar problems can happen when a bunch of people with no management skills decide to found a company and start hiring people.)