A Cretan named Epimenides once said: “All Cretans are liars.”
So if Epimenides is a Cretan and he is a liar, then the statement is false. But that means that Cretans tell the truth, and Cretans are in fact liars. So what is the truth? This paradox continues ad infinitum due to the self-referencing nature of the statement.
This is a well-known example of a logical fallacy, or a flaw in a logic. It is also referred to as the Liar Paradox, seen in: “This sentence is false”.
The power of a paradox is best portrayed in the following parable.
A wise woman who worked as a fortune teller was tried for being a witch. In her trial, the king demanded she tell a fortune. If the fortune was correct, she would be drowned. If the fortune was wrong, she would be burnt at the stake. The woman smiled, and replied: “I will be burnt at the stake”.