As a counterpoint to this, I interviewed at Google and was sure I had flunked. On every one of the follow-up questions, I didn't produce a working solution, let alone an optimal one.

I still got the offer.

Truthfully I do attribute much of it to luck. From what I have heard, most people had more difficult questions than I did, often with more strict interviewers. It's a high variance process for sure. If I were to interview for the same position now, I would most likely not pass the interviews.

Congratulations. I hope you enjoy working there. A close friend of mine used to work there in a very high position and they left after about a year or two, but left for what I consider to be pretty ridiculous reasons.

I'm not quite sure how much I could share without revealing their identity, but essentially they were sat down and told to work on their appearance. They had enormous technical chops (probably in the top 10 people in the entire world at what they do), but at least 60 lbs. overweight, no sense of style or fashion, etc., and as unfortunate as it might be to hear it... when you reach Director-level / C-suite positions, you need to physically project that OR you have to be so absolutely dominant at what you do that they cannot ignore you. They aren't that dominate.

A shame really, but they went off to work for a private startup and seem to be quite happy anyway.

I did okay in my interview with google but was passed over. The truth is they are always interviewing, so I think being hired has more to do with the timeframe of your interview than anything else. It's very similar to how the military drops many "requirements" of a soldier when what they need are bodies.

At some points, google is spinning something up, and at those points they need more devs, so they hire more of the interviewees. I think the rest of the process is basically random, based on the gut feelings of an entire team of random people.