It's very good for an idea to be commonplace. The important thing is that a new idea should develop out of what is already there so that it soon becomes an old acquaintance. Old acquaintances aren't by any means always welcome, but at least one can't be mistaken as to who or what they are.

No two people see the external world in exactly the same way. To every separate person a thing is what he thinks it is -- in other words, not a thing, but a think.