My reasoning is that probability does not define absoluteness. Base the probabilities on what evidence we have, but at the same time you have to consider bias, misinformation, and credibility. If we see the evidence and only the evidence, then yes his existence is most probable, but only probable. When you look at everything down to a minute detail and analyze the sources and the evidence themselves, then you really can't assume anything unless you were there. History is portrayed as one thing or another, which leads back to the saying, "history is written by the victor". In the next couple of centuries after the birth of Christianity, Christians made up two thirds of the Roman Empire, and eventually they were the top denomination when Constantine became the first pope. History is filled with bias, therefore one can not always see the full picture. Most probable leads to assumption that something happened, but just because we assume something happened does not make it fact. We have discovered no remains and no belongings. We only have mentionings and scriptures about him. No official roman, who were quite efficient at record keeping, record exists about him until Josephus' mentioning of him nearly a century later when Christians already made up a large majority of the roman people. All possibilities are accepted because nothing is certain.