A check
You cannot remember whether you have prayed three rak'ahs or four, and you have no way of settling it. On the maxim in this lesson, what carries?
The doubt, so start the prayer againWhat you last knew for certain, and you build on thatWhichever answer makes the anxiety quieterAsk somebody and do whatever they say
Yes
Certainty is not removed by doubt. There are specific rules for genuine uncertainty inside the prayer, which a scholar can teach you once and which are not the same thing as the endless doubt this course is about. What is never the answer is picking whichever option quiets the anxiety fastest, because that is the move that trains it.