I have heard many people say to break up when a silly mistake happens in a relationship from any of either girl or a guy. Isn't this wrong?

How can a true love and long lasting love form if people follow this rule? Why can't a silly mistake be forgiven by any of them in the relationship?
I have heard many people say to break up when a silly mistake happens in a relationship from any of either girl or a guy. Isn't this wrong?
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