Manjiro and Achilles cultures helped to shape them in different ways. Lets start with Manjiro. His culture shaped him to be respectful and relatively quiet but also a curious person. His culture taught him that he would have to follow the family line of jobs on his fathers side of his family. Achilles culture shaped him to be rather courageous and strong, maybe religious, but it also shaped him to be rather reckless. His culture taught him that if he went to battle he would most likely live a short life but be remembered by generations to come. Although, both of the boys cultures had a similar view on strength.
If Paul is interested in riding for Mr. Sutcliffe or racing, this sets up a conflict between Paul and his dad as his dad said Paul only rides horses that he knows - so he WON'T be riding Mr. Sutcliffe's horses.