A more thorough explanation:

The appearance doctrine is a legal principle that applies to cases of self-defense. It states that if a person reasonably believes that their use of force is justified, then that use of force is considered legally justified.

For example, imagine that a person is walking home late at night and sees someone approaching them with a weapon. The person may reasonably believe that they are in danger and use force to defend themselves. Even if it turns out that the other person did not intend to harm them, the appearance doctrine would protect the person who used force because they believed that they were in danger.

Another example could be a police officer who uses force to subdue a suspect who they believe is armed and dangerous. If it turns out that the suspect was not actually armed, the officer's use of force may still be considered legally justified under the appearance doctrine because they believed that the suspect was a threat.

The appearance doctrine is important because it allows people to defend themselves and others without fear of legal repercussions as long as their belief that force was necessary was reasonable.