They remember that the person isn't the behavior

When their partner does something hurtful or wrong, they criticize the action without pathologizing the human. 'What you did hurt me' is an honest statement about a specific event. 'You are a selfish person' is a verdict on someone's character, and it forecloses the possibility of change. The first opens a door to accountability and repair. The second closes it, because no one can argue their way out of a character verdict — they can only defend or collapse. This is a habit of mind that requires consistent practice, because it runs against the brain's tendency to essentialize: to take a pattern of behavior and turn it into a fundamental truth about the person. 'He did something inconsiderate' becomes 'he is inconsiderate,' and then becomes 'he will always be inconsiderate,' and eventually becomes a prison for both people. Mature partners make the distinction consciously, repeatedly, especially in difficult moments. The person they love is not the worst thing they've done.