I know what it means but how did the that phrase start?

It comes from Joseph Heller's novel of the same title, set in WW2. Catch-22 is a paradox, a kind of military rule, which is that if you are held to be crazy then you are kept somewhere safe where you are not allowed to fly missions. But the military thought a concern for one's safety in the face of immediate, real, dangers was the product of a rational mind. Now somebody would be crazy to keep going on missions, wouldn't they? Only a crazy person would do that.So the result is that, to the military, a person who is crazy stops being crazy if they volunteer to go on a mission. Once they are sane then they get sent on more missions but while they don't say anything and stay deemed crazy they won't get the chance. The moment they ask though, they stop being 'crazy' and get sent on missions ! That's the paradox: it's Catch 22

Fred,
Did you know that originally Heller's book was going to be called "Catch-18"? That was thought to be too confusing, because Leon Uris had a novel called " Mila 18."
"Catch-11" was also rejected because of the then recently released, "Ocean's 11."
The same with the idea, "Catch-17," which would have clashed with the title, "Stalag 17."

Kitty,
Wikipedia gives a good example of a Catch 22 situation:

In moving from school to a career, one may encounter a Catch-22 where one cannot get a job without work experience, but one cannot gain experience without a job.

And dg, they had to call the road 'Route 66' because it had to scan perfectly with 'get your kicks on...' (or so I heard).

Yeah,.. sure, Fred...prove your case!

THanks...I knew the book Catch 22 but thought it was called that because the phrase already existed.