The Need for Validation
When Cyril develops his theory about Shakespeare's muse, he reaches out to his friends for validation. In fact validation is not quite the word; it's more like he needs to be believed. And this struggle for external support drives him to take a lot of uncharacteristic action. For instance he commissions the forgery painting of Willie Hughes. Since Cyril is so convinced that he is correct and nobody around him believes in him, he starts turning his relationship to this theory into the most significant event of his life. Finally, he is driven insane and falls into despair because Erskine and the narrator and others refuse so adamantly to believe him.
The Role of Public Judgement
The character of Cyril dramatically embodies the relationship of the individual to society. He does not over-value public judgement, but he does fall under its veil. Because he is "effeminate" and spends his time in theater, Cyril is shunned and chastised by his grandfather and peers. He doesn't fit the mold of a typical young British man, so he is in some sense feared. Over time this understanding of how others perceive and refuse to accept him necessarily starts to affect Cyril's perception of himself. Perhaps this internal crisis, thrust on him by greater society, is what eventually drives him to strive for validation of his theory about Shakespeare. At any rate, Cyril makes decisions frequently based upon the desire to improve public perception of him. He wants desperately to be taken seriously.
Conflict of Ethics
Erskine and Cyril, though friends, run up against an inordinate amount of conflict throughout the course of this narrative. They are men ruled by different internal systems. For Erskine, the social and the entertaining take precedence over the personal sphere. He engages with the narrator on such an intimate level that he agrees to befriend and seek to understand Cyril -- a stranger, -- at the narrator's behest. They are trying to resolve an argument and eager to do so with deliberate action. For Cyril, however, the only truth is the personal experience. He is ruled by his need to create, to interpret, and to entertain. He is much less concerned with how one arrives at a conclusion so long as the conclusion is meaningful. As Erskine and Cyril interact, their opposing systems of ethics start to clash in increasingly devastating ways, as their opposition becomes a strain on both.