Ouija Boards. Why do they work for some people but not for others?

I am a born skeptic who does not automatically believe much of anything based simply on what other people say. If I am interested in something I have been told or read I will research it farther. That was true 30 yrs ago when I learned about Ouija boards. To my way of thinking, SOMEBODY had to be pushing it despite everyone saying they weren't. To prove SOMEBODY was cheating, myself and a trusted friend left the room and had the others pick out a random female name, with the stipulation that it could not be a name of anybody we knew. They wrote the name on a piece of paper my friend and I had also signed. There was no way of cheating because nobody could duplicate our signatures or change the chosen name after it was written due to using an ink pen. After they wrote the name on our pre signed paper, one person called us to come in after they had all left the room, taking the paper with them. We came back in and just the two of us sat down with the board to ask it what the chosen name was. Not knowing the answer ourselves there was no way we could cheat, yet the board correctly spelled out the name "Willow". Test was a success, but that success creeped us out and we decided not to play with it anymore. The exact same test was repeated later by people who were there or heard about it. Sometimes it worked and sometimes it didn't. I have my own theories as to why this is true, but would very much like to hear what others have to say about it. I am older and wiser today and can tell you from firsthand expierence that these boards can, but not always, cause a lot of trouble for people who mess with them. That much I know. What I dont know is why these things work for some people but not others. Its not due to religous belief either. After a heated discussion, I got a very devout adult christian to try it just so they could prove to me that it would NOT work with them. Well it DID work and I felt really bad for the guy because it messed his head up pretty bad......but it happened!! So whats the answer? Why some people but not others?