This film is very funny, but in parallel also is very serious, because I think it contains more truth and reality than simple or non experienced people can suppose.
Yes, courage can be a valor of double edge. Valiant soldiers and another people as policemen, firemen, etc, accustomed to deal with risk, no doubt have in real life these "battle fatigue" or nervous failures. Much persons suffer "panic attacks", not ever owing to an immediate danger, but to the continuous stress of life, work, family...
Only fictional men as agent 007 is free of these. Usually cinema shows only the other side of fantastic, but infantile unreal superheroes.
Instead, the clinical symptoms that shows the Paul Viti, the capo of the mafia played by Robert de Niro are fully credible. He's a real gangster and his violent life is a real, continuous stress and danger and, more than this, he must offer the external appearance of being a dangerous and strong man to the other capos and to have lovers he really doesn't need nor love only for pure ostentation. Final psychoanalitic explanation I find not believable but that's a minor detail.
And also are credible the courage of Ben Sobel the timid doctor played by Billy Crystal has to rejoin to deal with such a patient. Summing up, a movie plenty of good humour but furthermore, deep and more serious than usually thought, and I think underrated. An excellent and unusual film.