http://www.dailyreckoning.com.au/austrian-keynesian-bastiat/2008/02/15/

Frédéric Bastiat pointed to one: the belief that the destruction of wealth fuels its creation. He explains this by means of an allegory that has come to be known as the story of the broken window. Most famously it was retold as the opening of Henry Hazlitt's Economics in One Lesson, which is probably the bestselling economics book of all time.

A kid throws a rock at a window and breaks it, and everyone standing around regrets the unfortunate state of affairs. But then up walks a man who purports to be wise and all-knowing. He points out that this is not a bad thing after all. The man fixing the window will get money for doing so. This will then be spent on a new suit, and the tailor too will get money. The tailor will spend money on other items and the circle of rising prosperity will expand without end.

What's wrong with this scenario? As Bastiat put it, "It is not seen that as our shopkeeper has spent six francs upon one thing, he cannot spend them upon another. It is not seen that if he had not had a window to replace, he would, perhaps, have replaced his old shoes, or added another book to his library. In short, he would have employed his six francs in some way which this accident has prevented."

You can see the absurdity of the position of the wise commentator when you take it to absurd extremes. If the broken window really produces wealth, why not break all windows up and down the whole city block? Indeed, why not break doors and walls? Why not tear down all houses so that they can be rebuilt? Why not bomb whole cities so construction firms can get busy rebuilding?