Assuming you are referring to F. Scott Fitzgerald's novel, "The Great Gatsby," Nick Carraway is the narrator of the story and Tom Buchanan is a wealthy, arrogant, and sometimes cruel character.
One way Nick may reserve his judgment of Tom is by initially viewing him as simply "unaffected" by the world around him, rather than actively malicious. This is suggested when Nick describes Tom's "cruel body" and notes that he "hadn't seen [Tom] around" during his travels, implying a certain level of detachment from the world. However, as the story progresses and Nick learns more about Tom's actions and behavior, his initial reservations about passing judgment on Tom begin to erode.
~~~Harsha~~~