Have you ever heard of a paradoxical sentence like, "This sentence isn't true"?
I think it's a mechanics-of-language failure.
See, when we try to express an idea using language, it's often not possible to capture the pure essence of the idea.
There's concepts that don't have words for them and there's words that exist that describe a number of different things ("happiness"). Then, on top of that, there's structures and grammar and traditions and "implied meanings." When someone makes a sarcastic reference to "Mission Accomplished" you'd need to know a considerable amount of recent American politics and history to entirely get their meaning.
In the end, language exists to try to communicate meaning. It takes the thought or concept and puts it into verbal form. But because language does so many different things at the same time, loopholes and broken constructions emerge.
"This sentence isn't true" is around the borders of language, attempting to use a loophole to do something weird. It's a statement that identifies itself as the object, simultaneously looking to change the object by making the statement.
It's like dividing by zero. It doesn't work. How do you divide an apple into zero parts? You basically can't do it.
The same is true with our language. "This sentence isn't true" is playing around with faulty mechanics.