The creature realizes that people are automatically revulsed, even terrified, in its presence. This sets off a chain of events in which the creature really does become the monster it appears to be. Others' fear of the physically deformed, fear of the unexplained, and rejection turn the creature into a true beast. At one point it confesses (almost too eloquently for a monster) to Victor:

"I am thy creature: I ought to be thy Adam; but I am rather the fallen angel, whom thou drivest from joy for no misdeed. Everywhere I see bliss, from which I alone am irrevocably excluded. I was benevolent and good; misery made me a fiend.