This is a quote from Fitzgerald's story, A New Leaf:
New York, with its quality of many independent ladders set side by side, is unkind to even the meetings of close friends; so, in the case of strained relations, meetings are easy to avoid.
What's the idea behind the "independent ladders"? That people tend not to borrow from or lend things to each other, and are therefore not intimate?
I think the idea is vertical apartment buildings. By looking through windows, you can see intimate details of someone's life, but the trouble of going down several floors, across the street or alley, and up a similar number of floors is too much work to really learn about your 'neighbor' and become intimate friends.
The idea may be similar to silos in business that prevent communication between functional (vertically-integrated) entities. It is exasperated there because silos have no windows.
That would make for pretty crisp sound: New York, with lives inside stove pipe-liked structures rising side by side, is unkind to even the meetings of close friends…