I'd say after 7 years as a professional software engineer. I had never had to do anything harder in an interview than show up. The companies I applied too had prior coworkers and managers who wanted me on their teams. Then I ended up in a company where the management was so dysfunctional that it had the overtones of an abusive relationship. They then laid me off. At that point, I was a Sr. Software Engineer, during the depression, with a 2 week old newborn, out of work, stressed, not sleeping, and I had never white boarded a class, no idea what fizzbuzz was, and the last design pattern conversation I had had been 2 years previous.

I failed the interviews with some pretty decent companies. I got better.

My learning experience with that, is that the majority of interviews I took were not to determine if I was actually good at my job. They were to determine if I was good at interviews.