To me it just seems maddening, that Jewish leaders would really think that they could win any revolt against Rome, especially after Rome's response to their first revolt. Was there anything happening in the rest of the Empire at the time that might have led them to think that their revolts had a prayer of success?
Don't forget the unlikely Hasmonean victory of the Selucid Greeks about two hundred years earlier. Surely this was in the Jewish consciousness. In addition, there was a sense that Shimon Bar Kochba, leader of the revolt in 135CE, was the Messiah. Even Rabbi Akiva, who represented the rabbinic mainstream believed this. Messianism was surely fueling the belief that the Jews could win.