Islands stand out against a vast embrace of ocean, a negative space, an unconquerable space--therefore unconquered.
An oasis, likewise, blossoms forth from a great arid nothingness that could never mean anything permanent to any human being other than death.
Both are paradigm examples of something in nothing. Islands and oasis are loci of privilege: looking out at the ocean or the desert, the inhabitant feels oneself fortunate, strong, for trees and houses and churches stand at his back as he confronts the emptiness without. And, being within the scope of "something", all the rich ambiguity and subtle tints of somethingness are possible.

An enclave, on the other hand, is enfolded by positive threat: on each side a frowning menace, you feel a grip around your throat at all times, an oppressive clutch that may any minute tighten with throttling finality. You live by repeating the phrase "by the mercy of", you feel smaller, always, keep feeling smaller. Then smaller. Then nothing.
A nothing in something.
Under the shadow of overwhelming somethingness, the inhabitants of the enclave can no longer see beyond the yawning contrast between this nothing, that something. Only yes and no are the modifiers that are left them.

Thomas Schell* has come to see himself as nothing but an enclave: was his wife wrong to have believed that he could have ever become an island again?

*Oskar's grandfather