@Campbell it is more common than you would imagine. Apparently it's because of social media - we all feel inadequate, compared to all the people that seem great.
@Aleksandrs: I have written five technical books so far, I still have bouts of doubt and inadequacy when writing or at work. I use this feeling of not being good enough as a reason to do better next time.
Maybe he went home and went to bed. And took this tiny ad with him:
Building a Better World in your Backyard by Paul Wheaton and Shawn Klassen-Koop