… is from page 46 of Hayek’s The Trend of Economic Thinking  (Vol. 3 of Hayek’s Collected Works); the quotation appears near the end of Hayek’s brilliant 1933 essay after which this volume is named:
I don’t think that the work of the politician and the true student of society are compatible. Indeed it seems to me that in order to be successful as a politician, to become a political leader, it is almost essential that you have no original ideas but just express what the majority feel.
It follows that the successful politician will use academic economists and other ‘experts’ not as sources of genuinely novel ideas (be these good or bad) but, rather, only as authoritative props for whatever policies, good or bad, the politician has decided to pursue. This politician will, of course, choose for his or her academic props academics and intellectuals who truly believe whatever it is they are expected to say and write in support of the politician’s policy adventures. But policy is always driven overwhelmingly by the politician’s lust to get, maintain, and expand the powers of office and not by any original ideas that the academic expert brings in his or her role as policy advisor to the politician.