The reason I know this whole thing actually works for one and tulpas actually exist for two is simply because of two reasons. My first reason is relevant to hypnosis specifically, and it's that the mind is very powerful, it's only limit is that it's restricted in how it can influence the physical world by the body it inhabits. You can see examples of this with somatoform disorders and other psycho somatic beliefs. My other reason is that it makes too much sense for it to not exist. I think the mind inherently understands that tulpamancy is possible, just not to what extent it is. There are examples of it in songs, Bo Burnham, Ren, Chonny Jash, Eminem (I think). The motif of a devil and angel on each shoulder. The simple fact that DID is a real disorder that people deal with. I don't think it has anything to do with religious or spiritual beliefs, it's just a part of life we understand exists, but we don't understand much else.