In other words you cannot explain what it is you are talking about. It is true because I said so, right?

I would somewhat disagree with carl sagan. Why? Absence of evidence is evidence of absence when you are expecting it. If you would apply this quote on something that is completely unknown, which you cannot anticipate the outcome from absence of evidence, then it is reasonable to say we do not know what this means, hence we cannot rule out it's existence.