Why are dragons so often a knight's opponent in a fairy tale story Where exactly did these stories of knight vs. dragon come from?

Dragons are normally there to guard something, maybe treasure, Damsels, a secret item or scroll ETC.

Knights are not actually that brave...normal knights in medieval Europe were rude, abrasive, and drunk most of the time. They pledged to the king and the church, to serve each.

Before a person could become a knight, they would be a squire then a page.

These stories (I presume) would come from medieval Europe, passed down from generations.