REPETITA ...

Il segreto dell'invisibilità: il SEP (Somebody Else's Problem)

Within the novel "Life, the Universe and Everything", Douglas Adams character Ford Prefect describes Somebody Else's Problem as:

An SEP is something we can't see, or don't see, or our brain doesn't let us see, because we think that it's somebody else's problem.... The brain just edits it out, it's like a blind spot. If you look at it directly you won't see it unless you know precisely what it is. Your only hope is to catch it by surprise out of the corner of your eye.

The narration then explains: The technology involved in making something properly invisible is so mind-bogglingly complex that 999,999,999 times out of a billion it's simpler just to take the thing away and do without it....... The "Somebody Else's Problem field" is much simpler, more effective, and "can be run for over a hundred years on a single torch battery." 

This is because it relies on people's natural predisposition not to see anything they don't want to, weren't expecting, or can't explain. 

Geniale Douglas Adams, sempre.