In Through the Looking-Glass, Humpty Dumpty famously declares that words mean what he wants them to mean. I’ve known people to declare the same thing — that, for whatever reason, they can use their own meanings for words. (To be clear, Lewis Carroll was mocking the idea.)
While ideas matter more than the words used to express them, it’s a lot more challenging to communicate and discuss those ideas without a shared vocabulary. A common language that is rich and detailed makes the expression of ideas all the more precise and accurate.
This is why con artists prefer convoluted language: it’s a mask.