Hey ! Just wanted to clarify something. The feeling I got from my second round was that, when they ask "are you sure", it's because you're at least partly wrong. I got that "are you sure?" question and realised that I actually missed something. When this is the case, you need to say something like "Hmmm, let me take a step back here" and sum up your analysis points by points until you find something wrong (don't hesitate to add, at the end of each point you summarize something like "correct?", it'll make the interviewer participate to your thinking process and the occasion to step in if it's wrong). If you don't, not a big deal, at least you showed that you're not closed to criticism on your work and you don't hesitate to review what you analysed to see if something is wrong or not. At least that's the feeling I got, and a positive feedback I received on my interview.