From the Rulebook:
"The peasant is the base of society, and rarely takes up arms unless they feel oppressed or motivated to defend
Playing the Peasant mans that you are simply a poor layman who has taken up arms to fight. Something has you motivated to kill your enemies, and you will do so regardless of specialized training. Try to play as the oppressed and downtrodden, making people feel sorry for you and wanting to aid you in your quest.