Patsy Cline was not really a country singer.
At least that's what some people say. Her voice, at least in the view of long-time producer Owen Bradley, was best suited to the smooth tone of pop music in the 1950s and 1960s.
Still, Patsy herself was country through and through. She had always wanted to sing country music, and when she first started recording with Decca Records, she resisted Bradley's attempts to add thick instrumentation and back-up singing from the flashy group the Jordanaires, who also sang with Elvis.
But it was just that soft, sweet country music, light on twang and heavy on romance, that would come to define "the Nashville sound."
Remember, at the time when Patsy Cline was recording, the type of music she sang was still called "hillbilly music." Along with others at Decca, RCA, and Columbia Records, Bradley aimed to revise the bare honky-tonk sound that was popular in the early 1950s into something with more popular appeal. Although she appeared on the scene late in the game, Patsy Cline's diva-esque voice was a perfect fit for the Nashville sound.
Now, the Nashville sound is just a part of country music. And a whole lot of country music doubles as pop music. So, even though nothing really stands out to us now about the instrumentation on "Crazy," its popularity back then affirmed the success of that now-classic style and helped it make its way well into the mainstream.
The art of country music songwriting is like no other art. Instead of relying on clever innovation or pop catchiness, it relies on simplicity: great country songs are the ones that everybody wants to sing.
The gold standard for country song writing is Hank Williams: his songs are so timeless and covered so widely that you might not even know how often you've heard 'em. They've been adopted and adapted by countless singers, and sound good coming out of just about anyone who has talent.
Willie Nelson achieved the same effect with "Crazy." It's lyrically simple, but its theme—impossible love—is transcendent enough to make the song as relevant today as it was then. He also manages to fit the straightforward lyrics into a complex, showy tune, well suited to the likes of Patsy Cline.
In fact, "Crazy" fits her like a glove, so much so that the song's words and themes will probably forever be associated with her.