Matthew 26:33

‘But Peter answered and said to him, “If all shall be offended in (caused to stumble by) you, I will never be offended.” '

Peter was clearly upset at the suggestion that he would allow himself to be unfaithful. He protests that even if all the others prove to be so, he will not. He is not the stumbling kind. Nothing will move him from His Lord's side. And he no doubt meant it and believed it. Like the others he had no conception of what it was really going to be like, and of the weakness of his own faith in the face of Satanic opposition and the unusual methods of God. What was to happen would leave them all totally baffled, and in the end distraught. They would be battling with the unknown in order that through their initial failure they might learn in the end to overcome it.