Yank is undereducated; his own personal philosophies about "belonging" and his role in society are his only real driving force. Yank's lack of education is likely due to his childhood, which is only mentioned in passing; Yank speaks of running away from home while still a child to avoid "lickings," or beatings for disobedience. This was considered acceptable in the early 20th century, but since Yank removed himself from discipline, he had no motivation to learn or strive for higher education. Instead, he grew up "street smart," with his views clouded by a superiority complex based on physical strength.
"T'hell wit home! Where d'yuh get dat tripe? Dis is home, see? What d'yuh want wit home? (Proudly.) I runned away from mine when I was a kid. On'y too glad to beat it, dat was me. Home was lickings for me, dat's all. But yuh can bet your shoit noone ain't never licked me since! Wanter try it, any of youse? Huh! I guess not."
(O'Neill, The Hairy Ape, eoneill.com)
Yank's refusal to learn is based in his unstructured youth; without respect for authority, Yank probably dug in his heels whenever personal improvement was mentioned. His childhood also would have been focused on personal survival rather than learning, because he had no family to support him; his respect for strength would draw from his own experiences overcoming enemies. Yank's childhood was probably harsh and difficult, and his anger at the world is based in that adversity.