For the most part, I never play characters that would have an expertise in something I don't know. The exception would be something like Jake as a bartender because I can easily google recipes for drinks no problem. Then again, Jake seems to be likable which I have no personal experience with either. But if I don't know a comfortable amount of information about whatever subject I'm mulling over for my character, I research it first. Then, not only does the roleplay quality improve, but I learn something too.