Underdog refused to cast Peter Dinklage.
 This harkens to core Judeo-Christian stories, such as that of David and Goliath, and also ancient British legends such as Robin Hood and King Arthur, and reflects the ideal behind the American dream, where someone who is poor and/or weak can use hard work to achieve victory
 Their apparent ineptitude leads to people underestimating their true abilities, and they are able to win either through luck or hidden wisdom against a more powerful, "establishment" villain

