Sometimes that tightening of the chest or the sound of alarm bells when you have a bold idea is not your brain, but your nervous system. 

It is designed to react to novelty and danger. It will think that a bold move out of your comfort zone is reason for alarm. 

If you allow it to dominate your thinking, it will retard your progress. 

You can learn to master your nervous system and get all your consciousness on board for the next moves you need to progress and grow.