It depends on the definition of “working”

Driving back from St. Louis yesterday my wife and I were listening to old blues CDs. Listening to Muddy Water's "I've Got my Mojo Working" I started wondering about what he meant when he said he had his "mojo working." He had gone down to Louisiana to get it, he had it working but "it just don't work on you." Had it ever worked on anyone? By "working" did he simply mean that he had prepared it and was using it according to the instructions? Or did he know it was "working" because it worked on some people, just not on "you"? My wife is strongly of the opinion that he would only say it was working if it had worked on someone. I am not so sure. Would you say you have a magic spell "working" if you had set it into action, regardless of results? What do you think? I have put up a poll on this question over on the right.