I recently posted that The Tulpa Effect is my favorite concept in parapsychology. It is where a belief is strong enough to manifest in reality. This can be as petty as perceived increased strength and hair growth in someone who thinks they are a werewolf, or Pseudocyesis (False pregnancy) producing actual signs of pregnancy, to manifestations of haunting.
In reality my favorite concept in parapsychology is both the Tulpa Effect and Egregore. The concepts are strikingly similar but originally the Tulpa Effect was specific to the beliefs of a singular person while Egregore was a collective belief manifesting into reality. It's the difference between the little boy's belief in The Velveteen Rabbit being real, and Neil Gaiman's Sandman story, Dream of a Thousand cats or The Sandman: Overture, where if a thousand souls dream the same thing at the same time, it will change reality, including retroactively, to make that thing real.
In recent years the Tulpa Effect has been used to mean an individual belief or a collective so due to the evolution of language... or because of the Tulpa Effect itself (Ha!) the term is correct when applied to a singular person's belief or a group. When Googled, the Tulpa Effect most commonly comes up in regard to the belief in the Creepypasta character, Slender Man. (Note: due to the sources of where Slender Man lore came from and based on Jack Skellington's suggested identities in the mortal world, this suggests that they accidentally made the protagonist of Nightmare before Christmas real. I find this unlikely but amusing).
So, in conclusion, Tulpa Effect can be used to mean both an individual belief manifesting as reality, or a collective group's belief manifesting as reality, but the term Egregore should not be forgotten, as that was the original term to mean a collective belief manifesting into reality.
Side note: I wonder if because of pop culture and Egregore we have made various fictional monsters manifest. I muse about that when watching documentaries about the historic Dracula.
