In general, it can be stated that Nick is not a quite reliable narrator due to several reasons. For instance, he may not be present during a significant event. It means he can’t portray the situation subjectively. Nick might not be a trustworthy character. So, he always receives much attention from literary critiques. Everyone tries to understand his role in the story.
Detailed answer:
Unlike many other literary works, the narrator in The Great Gatsby is not the novel’s protagonist. It is one of the most apparent reasons why Nick isn’t a reliable storyteller for the reader. He is far from being the main character. So, Nick does not take part in all the events happening in the book. This fact leads to him being uninformed about certain situations. It means that he perceives events from a different perspective.
Nick is an observant narrator about body language and social encounters. But most of the readers are skeptical of him because of the way he starts the story. He doesn’t present the characters, nor he starts covering the novel’s main events in detail. Instead, Nick tries to prove that he is a reliable narrator to the readers. Nick spends a few pages on defending himself. All that effort is just to present himself as an honest person. One might argue that a trustworthy person would not have to prove anything to others.
Overall, we can say that Nick is not a reliable narrator. It generally is because he is not the main character and is insecure about himself. But his presence gives the readers a chance to focus on the protagonist, Jay Gatsby. Moreover, it is possible to analyze the main character’s nature. The reader can consider the descriptions and observations made by the narrator.