Craving

'The story is not quite so simple as that,' said the old woman, 'so many things happened after the eating of the apple. For one thing, the taste created such a craving in the man and the woman that they thought they could never eat enough of it; and they were not content with all the wild apple trees, but planted more and more, and grafted mountain-apple on to every other kind of tree so that every fruit should have a dash of that taste in it. They succeeded so well that the whole vegetable system of the country is now infected: and there is hardly a fruit or a root in the land--certainly none this side of the canyon--that has not a little mountain apple in it. You have never tasted anything that was quite free from it.'

'And what has that got to do with the card of rules?' said John.

'Everything,' said Mother Kirk. 'In a country where all the food is more or less poisoned--but some of it very much less than more--you need very complicated rules indeed to keep healthy.'
~C.S. Lewis, The Pilgrim's Regress, Book V, Chapter III, (1933)