A bus, half full of bishops and half full of economists, is travelling along a winding road through high mountains.

Suddenly the driver misjudges, disaster strikes and the bus plunges off the road, and starts its long, thundering descent over the edge of the cliff.

The bishops are terrified. They are by turns panicking and praying desperately. Then they notice that the economists are sitting calmly in their seats.

“Why on earth are you so calm? We’re plunging to certain death at the bottom of this cliff!” the bishops say to the economists.

“Well, it’s obvious” say the economists, “there’s such a clear need for parachutes right now that surely the market will provide them”.