War and constant death tend to breed fear. Add in a key ingredient of Catch-22, a bureaucracy that covers up ugly truths to seem competent and successful, and you've got a good recipe for paranoia. Characters in this novel have no trust or faith, and live in constant fear of betrayal. They read into others' actions too deeply and often assign them unintended messages. However unfounded their fears are, these fears have real consequences because those in power often act on assumptions with negative consequences.
Through his paranoia and refusal to fly missions, Yossarian demonstrates that he is a coward.
Despite his paranoia, Yossarian demonstrates that his fear is a rational and healthy, and is not a cause for shame.