There's no light the foolish can see better by

Another reminder that you cannot show to those who are determined not to see.

Image by Getty Images via Daylife

There's no light the foolish can see better by

Scienceblogs - Stoat

This is one of my favourite proverbs. I quite often find myself turning it over in my own mind as some particularly dense person fails yet again to see the bleedin' obvious.
And yet I discover that it doesn't appear to be a 'standard' proverb, at least as revealed by 5 mins of not-very-exhaustive google searching. If you know better, tell me.
The meaning, of course, is that once a certain minimal level of literal or metaphorical illumination has been shed on a subject, increasing the level of illumination or quantity of explanation will not allow the foolish to understand any more. Very useful for the GW debate.

I know it from John Crowley's masterpiece, The Deep. Perhaps Crowley invented it.