Everyone has their own view on the world and what happens around them. Maybe Bob believes that Humans Are Bastards. Maybe Alice thinks Chris is going to betray her. Given enough time though, these views and opinions can change, allowing Bob to see the good in man, and Alice to start to trust Chris. This trope is when that never happens; A character suffering from Theory Tunnelvision will stick with whatever idea he or she has for way longer than what would be normal. Even if Bob meets hundreds of Good Samaritans, he'll keep stating that Humans Are Bastards, and Alice will never trust Chris even though he saved her life several times now.