In an interview with Chuck Klosterman on the subject of crime, baseball analyst Bill James talks about how a person becomes a murderer:
It is not as if we walk through one doorway and decide that murder is acceptable. You have to walk through many doorways. The first doorway leads to a party, where people are doing drugs and having fun. The second doorway leads to more partying. It’s a long, long series of doorways, until you end up in a room where a terrible thing happens. So the question is, “How many doorways away are you?” It’s not a question about a person’s capacity to commit a murder. It’s a question of how many doorways we keep between ourselves and that situation.
The whole interview is really interesting.