Santa has 68 hours till Christmas. He asked an elf for a letter that he wrote, and that his editor said it had 13 mistakes. Santa, 2 hours later looked at the sheet of paper, and saw a tiny 13 at the bottom. Then he corrected all of his mistakes. But he saw only 12 mistakes. He realized that the thirteen was a mistake, but only to find out that if thirteen was wrong it would be imbalanced. Then the next day Santa fired his editor.
If there is x amount of mistakes told, but you find x-1 mistakes, if you change x to x-1 there is still another x to solve for. so in mathematical form x=x-1. It is a paradox because it will never be right.