Of course he was hesitant at first. He thought he had miscalculated, which he had. But then the A.I. makes him believe he had not miscalculated.
They played on his ego. What's easier to believe?? Your life's work is a success or a failure??
Oh, I completely agree that a closer comic book translation would have been better. But from the perspective of the movie, Octavius was very real, in that he was a man who was swept up in the ruthless determination he had to make his dream succeed.
The tentacles were like a devil on his shoulder. But ultimately it was his own vanity and humbris that was his downfall.
He was a very 3 dimensional villain, and he and Spidey came full circle by the end of the movie.
That's true. It is your WTF moment. But people overcome with stress or grief, thinking something that is not true, is hardly a strange concept is it??