Doubt of any sort can only be removed by action.
Other Johann Wolfgang von Goethe quotes:
A really great talent finds its happiness in execution.
Before you can do something, you must first be something.
It is not enough to take steps which may someday lead to a goal; each step must be itself a goal and a step likewise.
Knowing is not enough; we must apply. Willing is not enough; we must do.
If I accept you as you are, I will make you worse; however, if I treat you as though you are what you are capable of becoming, I help you become that.
None are more hopelessly enslaved than those who falsely believe they are free.
It is not enough to have knowledge; one must apply it. It is not enough to have wishes; one must also accomplish it.
Seize this very minute - What you can do, or dream you can, begin it, Boldness has genius.
To the person with a firm purpose all men and things are servants.
The best fortune that can fall to a man is that which corrects his defects and makes up for his failings.