If your time machine you preordered yesterday arrives today, you are able to go back in time and preorder yourself a time machine yesterday so it arrives today. This brand new time machine soon to be in your posession is a paradox, in that it is not actually ever made, and therefore never sold. It merely is. It is called into existence merely by thinking that if you had a time machine, you’d go back in time and preorder a time machine.

So what are you waiting for? Think hard now.