Adam Ozimek, on Butch Cassidy:
Security requires more violence than robbery because when you’re a robber you can make credible threats that actually prevent violence (“don’t move or I’ll shoot!”), and so you can avoid actually killing people. When you’re on the security side, once someone has decided to rob you they have already decided that the level of violence you are implicitly threatening is not enough to stop them, and so you have to use more violence than they were expecting to stop them