Zaroff also overestimated himself. His hunting experience led him to believe that he was more powerful than he really was. Although he knew that hunting a human would be more challenging, he thought more of his own ability than he should have.
Another lesson might be to never underestimate your opponent. Zaroff greatly underestimated Rainsford. He thought this would be the same fun and easy game he had played numerous times before. Rainsford was intelligent and far more capable than Zaroff gave him credit for. In the end, Rainsford was able to overtake Zaroff because of Zaroff's overconfidence and continual underestimating of Rainsford.