gavra-
Would you not agree that standing at har sinai during kabbalas haTorah constituted proof that it happened. Yet our ancestors who had that experience, sadly, just forty days later, went on to worship a golden calf and say the words “These are your gods, Yisrael who took you up from the land of mitzrayim. Now, I am well aware that there are many explanations as to what the actual sin was. However, no matter what it was, it certainly constituted a lack of emunah. Clearly, with all that proof, the nisayon of emunah had not been removed.