This means to take a single experience or piece of evidence and assume it happens all the time. So one way this can manifest on the Forever Alone scene is to filter/choose ones focus, to focus on a few inaccessible or shallow members of the opposite sex and apply their traits to all members of that sex — then draw conclusions about how hard it would be to meet someone. It could also be based on limited experience. Many people who are involuntary celibate have very limited dating experience, and IF the few encounters they did have were very negative and this can become a negative spiral of thinking and avoidance, but it is also a fallacy. At the end of the day, it IS a limited experience.