It's happened to me so many times, I should be used to it by now, but I'm not. I meet people who are involved in product development, and when I try to talk to them about user documentation I get brushed-off with "It's OK, we do all our user documentation in-house." "That's great," I say, "how many technical writers do you have on staff?"
"Oh no," they reply, "we don't have any technical writers, the programmers (or the engineers, or whoever) do it themselves."
These are intelligent people, who wouldn't allow anyone other than an experienced and qualified accountant to prepare their company's balance sheet, or anyone other than a qualified and experienced lawyer to prepare their end-user licence agreement, but they'll happily entrust preparing their user documentation to someone without any relevant experience or qualifications!