Knowledge: a double bind

"'Crawling at your feet,' said the Gnat (Alice drew her feet back in some alarm), 'you may observe a Bread-and-Butterfly. Its wings are thin slices of Bread-and-butter, its body is a crust, and its head is a lump of sugar.'

'And what does it live on?'

'Weak tea with cream in it.'

A new difficulty came into Alice's head. 'Supposing it couldn't find any?' she suggested.

'Then it would die, of course.'

'But that must happen very often,' Alice remarked thoughtfully.

'It always happens,' said the Gnat." (Carroll 1871, Through the Looking Glass, pp. 58-59)