"The session loses quorum.

If all the server instances become disconnected from each other, the session is said to have lost quorum. As server instances reconnect to each other, they regain quorum with each other.

If the principal server reconnects with either of the other server instances, the database becomes available.

If the principal server remains disconnected, but the mirror and witness reconnect to each other, automatic failover cannot occur because data loss might occur. Therefore, the database remains unavailable, until the principal server rejoins the session.

When all three server instances have reconnected, full quorum is regained, and the session resumes its regular operation"

Can someone explain, what exactly it means?