We require proof of existence because positive claims have to be proved. If there is no evidence for something, it is irrelevant and should be assumed false. For example, in Physics, nothing is assumed true, or fact, it is described as a "model" or a "theory".
I may not be able to prove my own existence, but my existence is ultimately irrelevant.
I may not be able to prove my own existence, but my existence is ultimately irrelevant.
