Confidence by its nature is smart and hardworking. It shovels fuel into the furnace. It is not cocky, conceited or arrogant. It's not stubborn or filled with boast. These are characteristics of something quite the opposite.
Confidence is secure.
Doubt, by contrast, is a stop sign in the middle of a flowing river. It's the brakes to the floor before your car gets moving. Confidence is a friendly and contagious spirit which enjoys the company of wonder. Continued active, thoughtful training, concentrated and undistracted, satisfies the wonder. You may never know a thing, but you begin to understand.