human behaviour of course relies on genetics but the environment a person grows up in plays the largest role of all..
an example , a professor had genetics that predisposed him as a psychopathic murderer, but he grew up in such a loving family it offset any violent predisposition
Maybe it's just a case of no one has jerked this guy's chain yet - then you might even hear the *snap*.
But we all have our snapping points (don't we?) given the right set of circumstances.