Why did the chicken cross the road?

“I have the answer,” said the terrifying voice. “ ’Tis not unlike the one that Thiazi baffled Grotnir with, five hundred winters agone. See you, mortal, a chicken is the human soul, and the road is life which must be crossed, from the ditch of birth to the ditch of death. On that road are many perils, not alone the ruts of toil and the mire of sin, but wagons of war and pestilence, drawn by the oxen of destruction; while overhead wheels that hawk hight Satan, ever ready to stoop. The chicken knows not why it crosses the road, save that it sees greener fields on the far side. It crosses because it must, even as we all must.”
[from Three Hearts and Three Lions, by Poul Anderson]