When on person sees an imaginary entity, they are the only person who responds to that entity.

However, if a real person fails to elicit any response from any person around them, would they cease to exist? Do they become imaginary?

Also, a person requires a world to live in. However, some people choose to withdraw from this world and create their own. I'm not merely refering to creative minds, such as writers, artists, or game designers, but more to hermits and self-outcasts. I have been isolated from the social scene myself, but not in a complete and utter sense; I still had people to talk to. Suppose someone chose to completely shut themselves out from the rest of the world. How much of an interior world would they create? And now the really fun, albeit sci-fi question. If a person really, truly believes in the world they create for themselves, and they have no outside stimulus to refute the existance of that world, does that world become real, in the sense that you or I could interact with it? Nobody really knows the power of the human mind, but simple belief has shown in many, albeit smaller, instances that it does hold some strange powers.

Hmmm... the latter gives me an idea for a cool movie.