Because a brain has been evolved for dealing with crude appearances which are supplied to its centers by imprecise and unreliable sense organs and for sloppy th

Because a brain has been evolved for dealing with crude appearances which are supplied to its centers by imprecise and unreliable sense organs and for sloppy thinking, good-enough for successful survival and reproduction (and necessary competition to accomplish that). Our minds are conditioned by appearances and the conditioning is based on the fact that things does not change too often in the physical environments - almost everything stays the same most of the time. The visual system, for example, has a lot of hard-wired heuristics which reflects this assumption. The cues which a brain machinery of visual cortex is utilizing to decode scenes is a perfect illustration how an evolved brain structure reflects actual physical environment in which it has been evolved. The mind, it seems, utilizes simple frequency-based machinery which strengthen (or weaken) the representation (whatever it might be, close to what we would call a weighted graph, perhaps) with each new impression. There is , obviously, no probability calculations going on in the brain, just simple weighted structures. Similar approach is in the very core of the classic machine learning. To alter the representation dramatically there must be some impression with a big weight, and this is what emotions are for. A dog getting sick after eating drugged food would learn to avoid it after just one single exposure. An emotionally charged experience is the simplest (and still the most effective form of persuasion, readily exploited by memes) because a brain has been evolved in to reflect the physical environment (its laws) and be adaptive-enough to survive mostly-stochastic, partially-observable environment. One single mention of a supposed fact is not enough to change one's internal representation of reality (which, perhaps, is a structure trained with thousands if not millions of impressions). Even direct experience sometimes is not enough, because one cannot completely trust ones senses. Only a rigorously trained mind could consciously deliberately alter its own model of the world (which is not that simple and cannot be accomplished at a whim) when it meets a single contradiction with "proven" or implicitly encoded in brain's heuristics laws of nature, leave alone a logical contradiction which is hard to notice given the default way of thinking we have evolved with. The non-verbal mind is much more ancient and much more powerful, and it does not understand the language of a newer parts.