Ignorance is a treasure of infinite price that most men squander, when they should cherish its least fragments; some ruin it by educating themselves, others, unable to so much as conceive of making use of it, let it waste away. Quite on the contrary, we should search for it assiduously in what we think we know best. Leaf through a dictionary or try to make one, and you will find that every word covers and masks a well so bottomless that the questions you toss into it arouse no more than an echo.
Paul Valery (1871 - 1945)
Source: Man and the Seashell (essay), Paul Valery Anthology
You have certainly observed the curious fact that a given word which is perfectly clear when you hear it or use it in everyday language, and which does not give rise to any difficulty when it is engaged in the rapid movement of an ordinary sentence becomes magically embarrassing, introduces a strange resistance, frustrates any effort at definition as soon as you take it out of circulation to examine it separately and look for its meaning after taking away its instantaneous function.