For three years or so I taught week long corporate training classes at Apple, Microsoft, Facebook, eBay, PayPal, Cisco and Intel. Every week, week after week, real rocket-science level Android and iOS deep-dive in to the guts of the operating system classes dealing with firmware and device drivers and file systems. In the classes we didn't build apps, we built operating system components. Small to large classes, thousands of software engineers from senior and up, over the course of those three years.

I would stand up in front of 80 or more engineers, go in to esoteric aresa of the operating and talk eloquently and at length about the structures and code found there, and live code on a projector, answering questions about the code and debugging the code of everyone in my class as they followed along. Day-after-day. 40+ hours a week. It was intense. I became an independent advisor to teams and a consultant for some of the groups on how to bring up Android on new devices, create device drivers, and so forth.

Some of those classes, I wondered how some of the people I was teaching was actually able to hold down their job.

Months later, after I stopped teaching, I interviewed at Intel and PayPal and Cisco. I bombed every interview. I was, by all accounts, unable to program my way out of a wet paper bag.

Everyone has off days.