The preist doesn't require anything. Your confession starts with "I confess to God, before you (priest, your witness)..." The only one you are cheating is the priest if you don't tell him everything. He will bless you and ask God to forgive you assuming you told God everything God already knows, and have resolved noever to repeat the same.
As you say, that's hardly the case, so we all tried to cheat God. But in many instances, we really don't see our sin because of arrogance and pride and have "nothing to confess."
Thanks for your comments.