A mirror cannot show how differently the same face appears to someone who feels safe beside it.

A mirror only returns geometry. It cannot show the face somebody sees when they are relieved you walked in, or how your expression looks to a person who has known it for twenty years, and that version of you is at least as real as the one in the glass. Self-assessment happens alone, without any of the information that makes a face mean something. What you inspect is a surface, and what other people meet is a person.

When the mirror is unkind, ask what a friend would see standing where you are. Their account is not flattery, it is evidence you cannot gather yourself.