You're an assassin,

[Cavernio]

born and raised. You've killed as a living your whole life, never hesitating once you've decided to do the deed, which also means never hesitating because you take your job seriously and would never accept a contract that you wouldn't do. You also don't just kill for others, but take tasks up on yourself, but all for the better good, not personal glory, money or achievement. (Twisted yes, but that's how you think. Think killing Hitlers or something if it helps.)

What might now, after so many years of close to perfection, cause you to hesitate killing someone that you strongly feel is evil or a threat?

Looking for help in the novel I'm working on now.