John Winchester could have prevented his son Dean's death in Supernatural. In season 1, John and his sons had the opportunity to kill Jenny, a vampire who later led a nest and killed Dean. Instead, they let her and another vampire go. John's failure to take the shot sealed Dean's fate.

The connection to John adds emotional resonance to Dean's death, as John forced his sons into the hunting business and raised them to become soldiers. The egotistical and arrogant mistake made by John in season 1 was later responsible for the death of his eldest son, showing how John doomed his son by making him a hunter in the first place.