I want to make sure the idiom "off the wall" means. I learned today about the idiom "off the wall". I want to know the origin of the idiom. In this idiom, preposition "off" means to be away from a place or postion and I guess "off the wall" means literally something is away from a "wall" and it refers that something is away from usual thing and it is different from other. Am I correct? If I am not, could you correct me? Thank you very much!