We see our world via our brains.....many people, especially within particular environments, are prone to imaginations which for them seem quite real...and this can even be a “shared” experience though it’s not real, rather an imagination of their own brains making which they may or may not want to imagine.
Also comes into play is a persons ‘desire’ to or not “see something”....we can so program our minds to think we’re are seeing if we strongly desire to do so.
I’m aware of a fellow who took hundreds of photographs of what he thought were entities visiting him....of course these ended up not being as he “hoped” for by any means....rather a form of vapor when conditions are good for them.
Buddhists claim that all the world is an illusion.
How do we determine what is real and what is not?