Arthur has to give up quite a lot in order to become a sailor on Augustus's father's ship and, as a result, realize his plan. First, Arthur Pym is basically a well-to-do young man with prospects and expectations that are dissonant to his wishes of carrying on a life at sea. Moreover, Arthur is neither the most courageous nor the strongest young man. Hence, his background and his personality would completely contrast those of a sailor. Still, he is adamant about what he wants, and his actions show more courage than initially expected.
Arthur would be giving up a comfortable life in Nantucket where his father, a businessman, has provided him with an excellent education. It is at school where he meets Augustus and his curiosity about life at sea begins to peak.
Moreover, Arthur's mother would never consent for her child to engage in such activities. He is also in danger of being cut off from the family fortune, as his grandfather is a successful attorney who threatens to disown him.
To achieve his plan, Arthur and Augustus write a fake letter that was sent to the Pym's. The letter is supposedly by Arthur explaining to his parents that he would be spend time at the homestead of some friends.
The problem is that the day that the voyage is set to depart, Arthur's grandfather is in the area. To escape him, Augustus gets Arthur aboard by cutting through his room and into a secret spot which is designed for hiding. Arthur remained in hiding until it was safe for Augustus to get him. After heartfelt farewells, the friends depart, and Arthur is able to accomplish his goal.