This isn’t just an epigram – life is much more successfully looked at from a single window, after all.
There are many life lessons in the novel that are passed over in a sentence or two. Nick had set out in his new life in New York, to become “that most limited of all specialists, the ‘well-rounded’ man.” Talented young men always meet life believing they can excel in all meaningful aspects, only to find that not only is the goal inaccessible, but the chase is unrewarding and draining. Fitzgerald recites the epigram, says it’s more than just that, and then leaves it at that. There’s a whole ‘nother untold novel in that sentence.
Also on this page, I love the poetic reduction of Long Island geography into “that slender riotous island” and “the great wet barnyard of Long Island Sound” with the “the bizarre and not a little sinister contrast” between West Egg and East Egg. The North Shore passed into literary legend on this page and has never been as glamorous since.