Doubt is an uneasy and dissatisfied state from which we struggle to free ourselves and pass into the state of belief; while the latter is a calm and satisfactory state which we do not wish to avoid, or to change to a belief in anything else.
The very desire to be certain, to be secure, is the beginning of bondage. It's only when the mind is not caught in the net of certainty, and is not seeking certainty, that it is in a state of discovery.