The answer is: The pilgrims drew lots and he drew the shortest straw.
In Geoffrey Chaucer's "The Canterbury Tales," the host and guide of the pilgrimage and owner of the Tabard Inn at Southwark comes up with the idea of telling tales to pass the time on the journey. Therefore, the pilgrims draw lots to conclude that the knight will begin. However, the narrator does not believe it is a matter of luck. In fact, the knight is the first character to be described because he is of nobility.