Answer:
1. If someone is in danger or a crime has been committed, or if you are required by law, or if they gave permission, or if it's not personal but might benefit someone else (like how to get something to work right).
2. If it is personal or might cause embarrassment, or the person has asked you not to tell anyone, or you signed something saying you won't tell, or you are not legally allowed to unless someone is in danger (like a priest or therapist).
Explanation:
There are other reasons, but these are the main ones.
