From "Google Glass: Artificial Unconscious?" by Neuroskeptic in Discovery Magazine (25 May 2013)
60 years ago, Ludwig Wittgenstein famously wrote:
Where does this idea come from? It is like a pair of glasses on our nose through which we see whatever we look at. It never occurs to us to take them off.
The “idea” in this case was a particular philosophical theory about language. Wittgenstein saying that other philosophers were making use of this idea without realizing it, unconsciously – so he chose the metaphor of glasses, which are always right before us, filtering what we see, even though we’re rarely aware of them.