Catch 22

When I was 17 I read Joseph Heller's Catch 22. It is based on a number of characters in the second world war who are flying very dangerous and risky flight missions as pilots. A lot of it was beyond me at the age of 17 but I understood the famous Catch 22 after which the book was named. Rather than try and explain it myself here is the description from the book:

"There was only one catch and that was Catch-22, which specified that a concern for one's safety in the face of dangers that were real and immediate was the process of a rational mind. Orr was crazy and could be grounded. All he had to do was ask; and as soon as he did, he would no longer be crazy and would have to fly more missions. Orr would be crazy to fly more missions and sane if he didn't, but if he was sane he had to fly them. If he flew them he was crazy and didn't have to; but if he didn't want to he was sane and had to. Yossarian was moved very deeply by the absolute simplicity of this clause of Catch-22 and let out a respectful whistle.
'That's some catch, that Catch-22,' Yossarian observed.
'It's the best there is,' Doc Daneeka agreed."

The term has now become part of everyday language and here is totally unrelated one from Groucho Marx:

"I don't want to belong to any organization that accepts me as a member."