My nomination for a Hayek quote for the AEA calendar is:

""The physicist who is only a physicist can still be a first-class
physicist adn a most valuable member of society. But nobody can be a great
economist who is only an economist--and I am even tempted to add that the
economist who is only an economist is likely to become a nuisance if not a
positive danger."

 From "The Dilemma of Specialization" originally published in Leonard D.
White ed. _The State of the Social Sciences_ (U. of Chicago Press, 1956)
and reprinted in F.A.Hayek, _Studies in Philosophy, Politics, and
Economics__ (U. of Chicago Press, 1967). The quote appears on p. 123 of
the reprinted version.

By the way, I seem to recall that the general sentiment of the Hayek quote
above was expressed previously by some great economist of the
past--possibly Alfred Marshall or John Stuart Mill.

David Mitch