A quick little article on why NATO expected to lose most of Europe to Russia in a conventional war:
http://nationalinterest.org/feature/why-nato-expected-lose-most-europe-russia-15267
When Stalin blockaded Berlin, all the chiefs of staff said give it away.
It's too isolated, no forces to push a relief force in, the NATO forces are hollow shells.
Truman accepted that a conventional land war was a certain failure, but he also couldn't cave on Berlin. That would just set the stage for the next land grab, probably Austria.
So they came up with the Berlin Airlift. The Sovs could have stopped it right away by shooting down some of the cargo planes, but their economy was really not up to a war. If NATO wouldn't roll over, they couldn't really dare to start a shooting war.
The real deterrance of NATO was to make it clear that no war would be a short one. As long as America stood with Europe, it would be a war that would take four or more years to end, and no serious Soviet planner believed they could last for that long.
These days, the West will just wag a finger at Putin and say "Okay, but don't cross THIS line or..."
^ What he said. O0
boiling the frog