Remember that YC backs founders much more than ideas. Also remember that they've already vetted both the founders and the idea, with the help of YC alumni, prio

Remember that YC backs founders much more than ideas. Also remember that they've already vetted both the founders and the idea, with the help of YC alumni, prior to the meeting. I would also imagine they have a strong aversion to BS and a well-honed BS detector. Ignoring the pre-packaged pitch you have spent months preparing and asking you some unexpected questions would seem to be a great strategy to quickly figure out what they really want to know - which may or may not have any relation to what you want to tell them.