Alexander Waugh

As a small boy strolling with his sister through a Viennese park one afternoon [Johannes Wittgenstein] came across an ornate pavilion and asked her if she could imagine it made of diamonds. ‘Yes,’ Hermine said, ‘wouldn’t that be nice!’
‘Now let me have a go,’ he said, and setting himself upon the grass proceeded to calculate the annual yield of the South African diamond mines against the accumulated wealth of the Rothschilds and the American billionaires, to measure every portion of the pavilion in his head, including all of its ornament and cast-iron filigree, and to build an image slowly and methodically until—quite suddenly—he stopped. ‘I cannot continue,’ he said, ‘for I cannot imagine my diamond pavilion any bigger than this’, indicating a height of some three or four feet above the ground. ‘Can you?’
‘Of course,’ Hermine said. ‘What is the problem?’
‘Well, there is no money left to pay for any more diamonds.’

Alexander Waugh, The House of Wittgenstein: A Family at War, London, 2008, pp. 25-26