Do you agree that saying one regretful thing can ruin a relationship forever?

Do we have to be very very careful with what we say, because people can change on a dime with their feelings towards us, even if there has been a long standing relationship between the people?

Have you ever had something said to you that you will never forget, and changed how you felt about someone? Maybe it made you feel like the mean thing said is the truth about how they feel about you, and everything said previously that was cordial and nice was false.

Or, something you regret saying, and lost a relationship because of it. Do you regret saying what you said? Are you confused why it was so terrible?

Do you think people who change their opinions so fast about someone are too rigid? Too extreme? Too sensitive?