Over at LewRockwell.Com, Aaron Singleton points out that sometimes the conventional economic wisdom is just plain not true.
At one time or another we became acquainted with the cliché, "money doesn’t grow on trees"... Now, for most people reading this (except the really ancient ones), this statement was an outright lie...Money does grow on trees, and in trees, and out of trees. It’s made of paper.
Monetary Myths [LewRocwell.Com]
Update: And, uhm, sometimes the conventional wisdom is true. As pointed out in our comments, our paper money is made of cotton. So it doesn't exactly grow on trees. It grows on Bushes.