Kearney interview questions

The most difficult questions were market sizing, and they played a "role playing game" "bad cop/good cop", one person that would put a lot of pression on you and a second that would be really nice. "Estimate the market for canvas in portugal" - But you are on a plane and cant contact anyone outside. Furthermore as i developed my answer they also developed more constraints for me to explore other options, like "imagine all canvas companies are private", "no company would share information", "imagine u would also sell paint and brushes along with canvas" and many things of the sort "Estimate the market for a private primary school network and say how it could be implemented"

Please describe the situation when you made a mistake and how did you resolve it?