"[Theories] are creations of the human mind, and they are not, however it might seem, uniquely determined by the external world. In our endeavour to understand reality we are somewhat like a person trying to understand the mechanism of a closed watch. They see the face and moving hands, but they have no way of opening the case. If they are ingenious they may form some picture of a mechanism which could be responsible for all the things they see, but they may never be quite sure their picture is the only one which will explain their observations. They will never be able to compare their picture with the real mechanism..."

        -- Albert Einstein