A parable about "obviousness" and CommonSense.

Suppose you draw a decent picture of an apple with good-enough shading to suggest roundness, and fax it to a friend. ET on Orion intercepts a fax of this drawing from Earth, attempts to interpret the apple drawing, and creates a 3D model. The resulting model looks kind of like a grey '''swollen loaf of bread''' with a knife-like linear ridge running the length of the loaf on top (the "stem"). If one looks at this loaf-like model edge-on, it indeed does resemble an apple, or at least the fax of the apple. Edge-on, the thin ridge lines up to look like a stem, for example. The loaf ends are rounded such that they generally match the shading in the drawing, but the ends are not spherical. 

You discover worm-hole travel and go visit ET at Orion. ET shows you his grey 3D model of the apple fax. You are confused and ask what it is. He then shows you the fax, and tells you it came from Earth. For a while you are perplexed, for the loafy model looks nothing like the fax to you. After a while ET shows you the loafy model edge-on (at least what we humans call "edge on"), holding up the fax next to it. It then finally dawns on you what happened and you then understand why ET's model looks almost nothing like a real apple. 

An Earthling "sees" an apple when they look at the fax because it closely fits with something they know very well '''from experience''': the apple fruit. Before the travel, it's unfathomable to you that ANY other intelligent being would see the fax and interpret it as something very different from the fruit: it's so clearly an apple. We humans would project our experience and internal notions to "fill in the gaps", such as how to "apply 3D" to such a drawing. We don't realize how "lossy" such drawings are because our mind so easily fills in the specifics as almost an '''unconscious reflex'''.

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http://www.art-made-easy.com/images/apple-tortillon.jpg
(Not quite the kind of drawing I had in mind, but close enough.)
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(I used "Martian" instead of ET in the title because ET-doesn't wiki-tize very well. Also, a Martian would be able to intercept our TV broadcasts and learn about Earth fruit in general, so I need a character that is more remote and that only happens upon a transmission. Maybe I should change it to "Alien and the apple", but "Martian" has kind of a fun retro feel about it.)
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See also: CommonSenseIsAnIllusion 
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CategorySubjectivityAndRelativism