Better be ignorant of a matter than half know it.

Partial knowledge is more dangerous than none, because it arrives with confidence attached. Knowing nothing keeps you cautious and asking, while knowing a little makes you act, advise and decide on a foundation you have not tested. Most bad calls come from the middle of that range rather than the bottom.

When you notice you are speaking from a half-formed understanding, say so out loud rather than rounding it up. Either go and learn the rest, or hand it to someone who knows. Admitting the gap costs a moment and prevents the sort of error that takes weeks to undo.