When hiring, how much does knowledge of your industry matter? It's a nice bonus, but in most cases it shouldn't be a driving force behind your hiring decisions. But too often I see hiring managers over-valuing this sort of knowledge, and hiring the wrong candidates.
If you hire someone smart and motivated, they will learn your issue or industry. Hire for the things you can't teach, like intelligence, work ethic, communication skills, integrity, and whatever non-teachable skills the open position truly requires. It may take your new hire a little extra time to get up to speed, but once that happens, he or she will blow away that mediocre candidate whose main advantage would have been starting out with industry knowledge.
I've been thinking about this because I was recently talking to someone who was hesitant to hire a seemingly great candidate because the guy didn't have any knowledge of or experience in the area they work in, and the job -- sort of a spokesman/grassroots organizing role -- would require him to quickly learn the topic inside and out. He was nervous that the candidate wouldn't be able to learn the area thoroughly enough, largely because he'd made a similar hire last year and that candidate had never managed to master the topic.
He, like me, is all about having candidates do simulations or exercises related to the work they'd be doing on the job, so he was contemplating asking the candidate to cram to learn the topic and then do a mock question and answer session with him on it. I advised him against it, because no candidate is going to be able to learn a complex, nuanced topic in a day or two, and he'd be testing the wrong thing; it wouldn't provide a realistic feel for how well he would do after spending a month on the job learning the issue.
What my friend should have been looking to test for was a specific type of smarts: whether the candidate could learn a complicated issue and make a compelling, intelligent argument for it, whatever that issue is. So why not take an issue he already knows well (you could let him pick or maybe there's something obvious from his background) and have him debate that instead? This would give a much better feel for how his brain works on a subject he's comfortable and familiar with -- it would reveal whether he can make compelling arguments, respond logically, shoot down straw men, be persuasive without being a jerk, etc. If he can do that for one issue, it's reasonable to assume he can learn another issue and do the same thing.
It seems to me this leads to a good way to evaluate what will actually matter on the job, and avoid making hiring decisions based on factors that really will only matter for the first month or so. Assuming you're not hiring for a position that truly requires a particular knowledge set (like, say, a pharmacist or an engineer), smart people will learn what they need to know. Test for smarts and hire for smarts.