Well, what would someone base belief on then outside of "knowledge, data, experience or other"? And how is "knowledge" defined?

If I give an example of something I believe in, say, a creator/god, whilst I may have never seen the creator with my human eyes, I believe in the creator because it makes sense for one thing (it stands to reason in my mind), and for another thing, there is "knowledge" or a knowing that comes from outside of myself and into myself. Something that does not correlate to anything physical like a piece of proof, but that "feels" right and as if I know it to be true.

An example of this is remembering a past life. If a human lived other lives at different or concurrent times, how would they know if they never saw that other life/body? Nor used any other physical sense to detect it? Yet there are many documented cases (with scientific-method applied) where small children remember their prior lives and the details they could in no possible way otherwise know, and which are then verified.

I myself have recalled pastlives with the aid of self-hypnosis (and spontaneous recall as well). And it is a matter of identifying with memory (which exists outside of the body) and bringing it into the brain. It feels like imagination because it is more similar to the process of imagination than remembering something that happened in the current lifetime. This is because memory of things from this lifetime have passed through one or more of the five sense and have left a chemical/physical trail in the brain - a pathway for retrieving or retracing the memory. It is the familiar route of remembering. But there is another way to get knowledge and that is through connection to the soul (higher self). This is also how I believe clairvoyance operates. The soul knows perhaps everything, certainly far more than the incarnate spirit.

Anyway, I bring this all up because belief can be based upon "knowledge" that is within the soul but that has laid no prior pathway through the physical brain. And this may not qualify as "knowledge" to someone who does not believe that memory and knowledge exists within the soul.

Another example of belief I have is in fairies, though I cannot say what fairies are exactly. I do believe in them, I have photographed what I know/believe to be fairies, and I have been educated on fairies, by fairies, whilst I was in an altered state of consciousness.

To sum up, IMO, belief is based on knowledge, and/or data and/or experience, but those things do not necessarily happen in this lifetime or with waking consciousness. I can't really think of an instance of belief where it isn't based on these things. Even a child who believes in Santa does so because they are told by their parents that Santa exists which constitutes data, and this is backed up by experience of sitting on Santa's lap and getting gifts.

For me, I actually believe in everything because I believe in infinity. The thing about belief is it can be malleable. You can add to it or take away from it as you go, but it provides a great base and lots of ladders to get you to other premises and ideas. Belief can be freedom from boundaries, which I should think appeals to you. And yet it does not, right?