It's a shame that so few people in the fandom talk about this quest ("The Final Trial"), or at least these two lines of dialogue.
The quest does an excellent job of showing why Lambert is the way he is. It gives us insight into his worldview, his values, and what he believes he is owed after what Destiny has taken from him (even though he openly claims not to believe in it).
I also think it would be interesting to analyze this quest alongside "Following the Thread", since he mentions drinking alone earlier (Geralt doesn't ask him about it, which is a shame [*1]), and we know how important Aiden was to him. Perhaps it was the loss of friends like Aiden (and Coën?) that made him even more cynical and sarcastic than he is in the books (at least to me it seems so).
This particular quest, however, also shows why he dislikes Vesemir and deliberately avoids him. Lambert is his Child of Surprise, and I’ve never seen anyone mention it in fanfics or posts.
([*1] dialogue about drinking)

















