Terry Pratchett hasn’t been an escapist writer for quite some time.

He’ll amuse you, sure, but he won’t tell you that things are great just the way they are or that they’re hopeless and there’s nothing you can do. He’ll tell you that you — yes, you — should make them better.

And then he’ll do something even more radical. He’ll make you think you can.

-- randombrethren, Tumblr

One of his (Sir Terry) sources for inspiration was Brewer's Dictionary of Phrase and Fable [0]. Indeed he wrote a foreword for one of them.

[0] Brewer's Dictionary of Phrase and Fable