"You mean there's a catch?"
"Sure there's a catch", Doc Daneeka replied. "Catch-22. Anyone who wants to get out of combat duty isn't really crazy."
There was only one catch and that was Catch-22, which specified that a
concern for one's own 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.