A question came from a user who shares a calendar with others and wants to show some of his private appointments to some of the people who have access to his calendar.
In order for another user to see appointments you've marked private, you need to give them delegate permission to the folder and give them permission to see the items marked as private. This is an all-or-nothing deal; you can't give them permission to see some of the private appointments, while still keeping some appointments hidden.