Neil and Vincent are orderly men, and Mann harmonizes their activities beautifully, but being human isn’t an orderly business. Opening up to other people means opening up to chaos and disorder.
And from the later forum discussion of Heat:
It struck me that, for all the ways Heat questions the macho code of non-attachment that McCauley and Hanna live by, it has a very old-fashioned view of the uses of violence. Both McCauley and Hanna deploy it very precisely. What’s wrong with Waingro is that he can’t control himself.