"It is no crime to be ignorant of economics, which is, after all, a specialized discipline and one that most people consider to be a 'dismal science.' But it is totally irresponsible to have a loud and vociferous opinion on economic subjects while remaining in this state of ignorance."
It is chapter 3 of Ludwig von Mises's Human Action.
Robert Murphy has written a study guide for this chapter, complete with summaries, technical notes, annotations of key contributions, and study questions.
His study guides are also available in PDF for the following chapters: I, II, III, IV, V, VI, VII, VIII, IX, X, XI, XII, XIII, XIV, and Mises.org continues to post more as Murphy writes them.