A secret is a powerful thing. The holder has power over the subject for the duration of the secret’s existence. The subject, or subjects, of a secret are diminished. The power of a secret can be crushing, particularly if the holder and the subject are one.
Revealing a secret releases its power. The release can be either good as healing or restorative; or it can be negative with unwanted revelations, damaged reputations, and torn emotions. The holder of the secret has the power to decide which effect to use.
Perhaps the biggest power a secret has is the ability to force individuals into making choices. Think of the lies that are told to keep a secret. A lie gets its power from the secret it conceals the truth and is not itself the truth. Revealing the truth destroys the power of the secret.
Secrets are everywhere and judicious use of them can be good or evil. Story characters can be driven to good or evil choices by them; forced to lie, and keep more secrets; or choose to reveal a secret, thus freeing the secret’s subject from its bond. For a writer, secrets are a powerful thing.