Never the twain shall meet
Definition 1 of 1
Pro Tip 1/3Cultural Origin
The phrase comes from a Kipling poem highlighting East and West cultures' differences. 
He's from a rural background, and she's a city-dweller; never the twain shall meet.
Pro Tip 2/3Idiomatic Use
It's mostly used in spoken language to emphasize a sharp contrast. 
As a minimalist, she avoids flashy cars—never the twain shall meet.
Pro Tip 3/3Metaphorical Gap
Think of it as expressing a metaphorical distance that cannot be bridged. 
In terms of politics, they are on extreme ends; never the twain shall meet.