I’m guessing he had a few other happy habits. For one thing, those 9 kids kids didn’t make themselves. 
Not quite. He also liked beer.
To the OP - you aren’t the only person who, while doing something you’ve done a million times before, has a subconscious that slowly changes from “I got this, it’s as natural as breathing,” to “Suddenly I’m conscious of my breathing,” to “I’M WORTHLESS AND INCOMPETANT AND EVERYBODY HATES ME.”
Meanwhile, your autonomic nervous system is happily humming along, continuing to perform as always and no one can see that you’re wracked by self-doubt and feelings of inadequacy. You know what? Sometimes your autonomic nervous system knows best.
I hear the voices. It’s many in my head. I generally cook up something to tell to shut them up😳
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And then I do whatever I want. They can go blow. I don’t care.
Seriously, don’t sweat it. Everyone has doubts.
Push your singing voice out there and they’ll fade.