Why is Pelias worried about a one sandaled stranger?

Pelias is worried about the one-sandaled stranger because of a prophecy he received, which foretold that a man with one sandal would come to challenge him and ultimately lead to his downfall. This stranger is Jason, who lost a sandal while helping an old woman cross a river. Pelias fears that Jason's arrival signifies the fulfillment of the prophecy and poses a threat to his rule.