"Another thing I have learned since 1968 is that one should emphasize as early as possible that although objects moving at the speed of light famously behave in some very strange ways, the behavior of objects moving at speeds comparable to the speed of light can be just as peculiar. The peculiarity of motion at the speed of light is just a special case of a more general peculiarity of all motion, which becomes prominent only at extremely high speeds. That more general peculiarity can be expressed by an elementary but precise rule that it is possible and useful to formulate at a very early stage of the subject."