While entering a new field, you should be aware that there's at least an iceberg of ignorance you have to deal with. As you correctly noted, it's hard to tell which kind of mistakes this ignorance will lead you to make, but your prior for making mistakes should in general be pretty high. What I'm trying to tell is that you should be able to preemptively deal with the discovery of the tip of the iceberg: you should expect it to pop up at some point. Other people should in general be aware of it too; if they don't, just point it out beforehand. Usually the "I don't know how to do it, but I am willing to learn" position is the best one, and it's normally socially acceptable (except if you have previously sold yourself as an expert on the subject). Even if someone forgot how it was to be a newbie, he should know deep down that the only way to get rid of the iceberg is to slowly liquefy it: start small, get rid of the first tip, and then proceed to get rid of whatever comes to the surface next.