'I know my father' and 'I don't know the masked man' can both be true of the same person
The masked man fallacy, traced to the Stoics and revived by Descartes, shows why you can't freely swap two names for the same thing inside a belief statement. You might know your father without knowing that the masked man robbing the bank is your father, so 'I know X' and 'I don't know Y' can both be true even when X and Y are the very same person. The puzzle exposes a gap between what's true of an object and what's true of how we refer to it.