Wrongdoing is a slippery slope.

Setting boundaries for behavior only works if a person stays within the lines. Fettes is morally ambiguous as a young man, but he has a clear sense of right and wrong in terms of self-preservation. He knows not to do anything truly heinous to protect his reputation. However, he moves his ethical lines under the influence of an older student, Macfarlane. Once under the thrall of Macfarlane, Fettes’s wrongdoing escalates dramatically. Whereas he first intakes bodies from obviously shady men, he then assists in graverobbing. Finally, he ignores evidence and co-conspires in acts of murder. Fettes’s willingness to keep moving his boundaries demonstrates how crime and immorality create a slippery slope. Once begun, as Macfarlane assures Fettes, wrongdoing escalates to cover up former deeds, leading to even greater acts of evil. 

Macfarlane likewise demonstrates how criminal and immoral behavior leads to more and often worse acts. The man’s origin story is not provided, and he is introduced only after he has already compromised his morals and ethics. The dinner with Fettes and Gray reveals a moment that suggests Macfarlane has never actually murdered anyone before. When Fettes jokes about enemies ending up on the dissection table, Macfarlane jerks up his head, implying that he is considering murder for the first time. When he appears at the lab door with Gray’s body, it’s clear that he has crossed a boundary and committed murder, showing the escalation of his wrongdoing. In his reunion with Fettes at the George, it’s implied that he’s still willing to do unspeakable acts for his own profit, including hurting or even killing others to protect himself during his interaction with Fettes. The progression of his actions illuminates how his immorality and unscrupulousness have grown throughout his life.

Ignoring the truth is an act of will.

In the telling of his dark tale, Fettes demonstrates how ignoring the truth is an act of will. Fettes rationalizes his immoral behavior by assuring himself that the ends justify the means. He knows drinking and engaging in acts of debauchery are wrong because he is careful to avoid doing anything so bad that he damages his reputation or compromises his future plans. Because he can maintain that balance, he ignores the immorality of his behavior. Later, he performs duties for Mr. K— that are clearly suspicious, but he rationalizes that he’s currying favor with a powerful professor, and he will ultimately benefit from the arrangement. When faced with what he considers indisputable proof that Jane Galbraith is a murder victim, Fettes willfully allows himself to be persuaded by Macfarlane to ignore the evidence and continue doing his job. Fettes is faced again and again with facts that he willfully ignores for his own gain and convenience.
 
Sometimes there are competing truths, and it takes an act of will to ignore the most compelling one. When Fettes is confronted with the truth that he has been involved in illicit activities, his most important truth is that he will suffer consequences if he disengages from or reveals what’s been going on in the lab. Instead of choosing the ethical and moral truth to focus on—that people are being murdered—Fettes acts on the other truth. He acts on the fact that coming forward could lead to unpleasant consequences for himself. He is consistent in this willful choice because he never exposes Macfarlane and instead leaves medical school without taking responsibility or revealing Macfarlane’s actions. This choice is evident because Macfarlane has flourished and prospered over the years. Because he willfully chooses to ignore the truth that led to bad moral and ethical decisions, Fettes is tormented and suffers from the knowledge that he made the wrong choice. 

Pride makes people vulnerable to influence.

Macfarlane can manipulate Fettes because Fettes’s pride makes him vulnerable. Macfarlane skillfully utilizes peer pressure to ensure his classmate’s complicity and silence. In the matter of Jane Galbraith, Macfarlane handily tips Fettes into complicity by appealing to his pride. He says if Fettes is worldly, sophisticated, and experienced, he will clearly understand that he should maintain his silence. Macfarlane further appeals to Fettes’s pride when he suggests that they were both specifically chosen for their jobs by the illustrious Mr. K— because they are not cowards but rather strong and brave men who know how to do a job and see it through. Fettes is immediately persuaded and agrees to do as Macfarlane says, showing that Fettes is weak from his own pride and easily influenced.

Fettes’s ego continues to make him vulnerable to Macfarlane’s influence to the point that Fettes ultimately considers his criminal activity a point of pride. After being manipulated again to maintain his silence after Macfarlane’s murder of Gray, Fettes eventually boasts about his complicity. He is so under Macfarlane’s power that Fettes claims that his friend is making a man out of him and that he was nothing before he knew Macfarlane. Fettes continues, bragging about his ability to ignore the horrific acts he has seen and been a part of. He has been so vulnerable to Macfarlane’s influence that he mocks Gray’s death and celebrates how he benefits from his criminal activity, patting the gold in his pocket. He arrogantly boasts about how he has no fear of God, the devil, or any other kind of judgment because his pride has been so inflated by Macfarlane’s influence.