If you can't live with what you are doing or have done already then you won't

 I was thinking about this as I'm watching the 2nd season of "The Black Doves" with Keira knightly.

And how when often operatives meet their end they are prepared for it almost like they were always "suicidal Homicidal" always which is a category which comes from being suicidal.

So, being an assassin is usually someone who is basically suicidal but who is afraid to kill themselves and waiting for someone else to kill them. When you kill there is an inherent need to be killed at some point because you cannot live with the fact that you have killed one or more people.

So one of the most important things we all have to live with in life is how we treat others. Because how we treat others we will always tend to treat ourselves too (EVENTUALLY) simply because this is the nature of being a human being.

So, when people are unnatural enough to kill others they usually might be unnatural enough to slowly  or quickly kill themselves too.

This seems to be the basic nature in people everywhere I have been on earth.