If you are 75% good, your counterpart will be 75% evil.
If you are 99% good, your counterpart will be 99% evil.
What do you do if you meet your evil counterpart?
If you are 75% good, your counterpart will be 75% evil.
If you are 99% good, your counterpart will be 99% evil.
What do you do if you meet your evil counterpart?
Kill him. There can be only one.
Oh God, I believe that makes me the evil one. What do I do?
Killing villains doesn’t make you evil. Unless you were already evil which would make your counterpart good, and killing them is just in your horrible nature.