First story bias

Term describing a mindset of a person when they are unable to see another viewpoint/or the truth in a situation. It's when a person has heard about a "story, opinion, or report" from one person first and believes that this is the truth. This occurs when a person's mind is closed and incapable of hearing and understanding another viewpoint or report because they completely believe what they were told initially about a person or situation is the truth.

John's girlfriend believed he had cheated on her because her best friend told her she saw him with another girl. John was not with the other girl but his girlfriend had "first story bias" and felt she could not trust him anymore.