Andrzej Sapkowski said this quote

You can't stop a soldier from being frightened but you can give him motivation to help him overcome that fear. I have no such motivation. I can't have. I'm a witcher: an artificially created mutant. I kill monsters for money. I defend children when their parents pay me to. If Nilfgaardian parents pay me, I'll defend Nilfgaardian children. And even if the world lies in ruin - which does not seem likely to me - I'll carry on killing monsters in the ruins of this world until some monster kills me. That is my fate, my reason, my life and my attitude to the world. And it is not what I chose. It was chosen for me.