Assurance is a measure of your conviction in the usefulness and success of your goal.

It differs from ambition or willpower in that it acts passively. You can’t will yourself to be sure of something. You either are or you are not. Willpower usually defeats the purpose.

Assurance, like muscle memory, acts in an unconscious and unquestioned fashion. 

Once gained, it sinks beneath the threshold of thought and is available to you going forward, like the ability to read, write, walk, grasp for objects with precision, or ride a bicycle.

Assurance grows with practice, and success breeds more success. Before success, it’s a bit of a Catch 22. Luck gets involved, instinctive recognition of inborn skills, getting the right guidance.