Do I have my head up my own arsehole?

Do I have my head up my own arsehole?
What is self-doubt useful for?
To what extent is it healthy to doubt myself?
Would I achieve more if I doubted less?
What measurements of my own performance should I value?
What measurements of my own performance should I adopt as "my measurements"?
What about the state of the world would it be valuable to be measuring?
Or what measurements of the state of the world, would it be valuable to be paying more attention to, or less attention to?
What measurements of my own performance would it be valuable to be paying more attention to, or less attention to?