Dark Secret

From Age of Intrigue Wiki

This is a normal challenge that can grow heavier depending on what the dark secret is. To count there must be a risk that your dark secret is exposed during the game. A dark secret is only a dark secret when it truly haunts you.

When exposed the dark secret must provide a considerable disadvantage such as loss of reputation, being brought before the law, losing one's title etc. etc. The more devastating the result of exposure, the more major the dark secret is. If you seek the compensate the dark secret in other elements of your character to minimize damage, it is not as effective and thus drops to minor.