Having never used a board myself, why does it require a group?
When I was about 4 I had a dream about one of my great grandmothers. She was very old and lived in a trailer in another state. I may have met her two or three times in my short life.
In the dream I was in her trailer. It was night and I was standing by her bed. An eerie light was shining through the window, which was open but covered by a cream-colored silk cloth. A breeze was blowing through the window, enough to make the cloth flap.
My great grandmother was lying on the bed, which had the same sheets as the one on the window. I remember they had a sheen to them. The breeze was blowing the sheets, which would have been blown off the bed if they had not been tucked partially under her leg.
In the dream I was scared of her body, but for some reason I had to stay by the bed alone all night. In the morning I stepped out of the trailer, down the two steps, and into the morning sun. My mom went into the trailer and came out, telling everyone that great grandmother was dead.
In reality she died that night. I never told anyone my dream and when it occurred until I was in my 20’s. I’m 30 now, and I can’t believe how vivid it is to me still.
Anyway, sorry for the long story.
It requires a group because the movement is caused by changes in the net forces on the wand. If you are operating alone, you know you’re the sole cause of every movement of the wand, and there’s no trick to it. If you do it in a group, no one person can fully know all the forces on it. It’s in dissipating the responsibility throughout the group that enables the psychological trick to work.
HOWEVER
The more dissociated someone becomes from their own influence on the wand, the more external the wand’s behavior appears. Providing insight into subconscious desires becomes a reward for developing this psychologically dangerous dissociation. The user may actually convince themselves that some completely external force is responsible, allowing the dissociation to become coupled with an almost psychotic delusion.
And those dangers are even discounting the demonic dangers! According to the “magic,” the ouija board channels spirits to come among practitioners. If such spirits are demonic (and to whatever extent they are real, they would have to be demonic since divine spirits would not participate), this is merely inviting demonic influence. The spirit does not enter any given individual. However, when practiced alone, the spirit’s influence is only through a single person. Thus, the spirit comes to be entirely within a person. This, then, isn’t merely influence, but possession. Even ancient practitioners considered going solo to be taboo for this reason. (If you don’t believe in demonic possession, you could suppose this is merely an explanation for why solo practitioners went psychotic.)