Flemming blogs about "how we can physically perceive that which we assume we'll perceive and that which we've been conditioned to perceive".  Quoting from an article by Howard Bloom, that speaks of several experiments that suggest how powerfully groups can shape what we think reality is, he says :

"...  our reality is formed and manipulated by what we hear, what we remember, what other people seem to believe, etc. Not just that our memories and peer pressure is influencing and coloring how we see the world. No, much more tangible than that. We physically perceive that which we assume we'll perceive and that which we've been conditioned to perceive. I particularly find experiments such as these fascinating:"

".... so, does that mean we're all just gullible sheep who're walking around in a trance, thinking we see things that aren't really there? Well, to some degree, yes. But we can start becoming conscious of our processes of perception, aware of how realities are generated, and we might actually catch when we're being mislead by words or memories or other abstractions. And we might learn to always expand our sense of reality, reaching beyond the hallucinations generated by our assumptions, beliefs and memories."

So true Flemming ... whichever way ... either by imagining what does not exist or by closing our opportunity to sense what does or can - we unfortunately wear these blinkers most of the time.  And we can go through life missing the real power of our own reality or our own truth, of our own ability for stretch.   

This thought came to my mind - often quoted but i think appropriate here ...

"Do not try and bend the spoon, that's impossible. Instead only try to realise the truth. (What truth?). There is no spoon, (there is no spoon?) then you'll see that it is not the spoon that bends, it is only yourself" ....  from The Matrix (the original).

Check this out too - on the fallibility of perception.