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. Six weeks or eight weeks of training are miserably lost if you vacillate, wonderfully invested if you trust. Whether your techniques are worthy or not, you are. Trust your efforts and you'll grow.