Andrzej Sapkowski said this quote

It's an invention, a fairy tale devoid of any sense, like all the legends in which good spirits and fortune tellers fulfill wishes. Stories like that are made up by poor simpletons, who can't even dream of fulfilling their wishes and desires themselves. I'm pleased you're not one of them, Geralt of Rivia. It makes you closer in spirit to me. If I want something, I don't dream of it—I act. And I always get what I want.