7. The Vervain Access
Vervain was introduced as a rare element that can keep vampires from compelling humans and can also burn a vampire. The rarity of vervain was actually stressed repeatedly when it was first introduced but eventually, it seemed like everyone had access to this effective plant.
Throughout the course of the show, almost everyone seemed to have quick and easy access to vervain and had even accumulated enough vervain to contaminate the town’s water supply. This major error was overlooked by fans as most viewers never questioned how did Mystic Falls stumble into an overabundance of vervain?