The Great Gatsby, subtly unadaptable

What is the meaning of "subtly" in this extract from the last chapter of The Great Gatsby?

. I am part of that, a little solemn with the feel of those long winters, a little complacent from growing up in the Carraway house in a city where dwellings are still called through decades by a family's name. I see now that this has been a story of the West, after all—Tom and Gatsby, Daisy and Jordan and I, were all Westerners, and perhaps we possessed some deficiency in common which made us subtly unadaptable to Eastern life.

Thank you.