By the way, I tend to be quite good at these "whiteboard" style problems and I always make mistakes. Every single time. I get the impression that most interview

By the way, I tend to be quite good at these "whiteboard" style problems and I always make mistakes. Every single time. I get the impression that most interviewers would find it weird if you didn't, because they didn't get to see you think critically about something you've never seen before. A seriously underrated skill (which you can practice) is keeping calm when you make a mistake and reasoning out loud, under pressure. When you hear yourself saying, "Oh wait, that won't work because..." is when you know you're on the right track.