It is about the story of Captain Joseph Yossarian（尤索林） and his attempt to avoid serving in World War II by feigning（假装） insanity（精神错乱）. However, Yossarian is thwarted（反对，阻碍） by the doctors argument that if he were truly mad then he would endanger his life and seek to fight more missions.On the other hand, if he were sane （健全）, then he would be capable to following orders to fight more missions. Thus the phrase catch-22 came to mean a proviso（限制性条款） that trips one up（绊倒, 使失败, 挑剔） no matter
