Confidence can be borrowed and competence cannot. Acting assured will get you into rooms, and there is a real place for that, but the moment arrives when work has to be produced and the performance stops helping. What the advice leaves out is the part where you urgently have to learn the thing.

If you have talked your way into something, use the gap well. Work out exactly what you will be asked to do and close the biggest hole first, this week. Asking a direct question early costs far less than being found out later.