… is from page 42 of economist Lionel Robbins’s excellent and still-relevant 1937 book, Economic Planning and International Order (footnote deleted):
When Mr. Keynes, the other day, urged that “goods should be homespun wherever it is reasonably and conveniently possible”, he was urging that the ports of the world should be allowed to decay and that ships and international railways should be devoted chiefly to carrying passengers…. It means, too, the decline of all those industries which have specialized in producing for export, the agriculture of the New World, the manufactures of the Old. The Lancashire cotton industry must henceforward look chiefly to home markets. British engineering must no longer seek a market for foreign parts. For a very long time to come, national planning in this sense means, not merely the protection of home industry, it must also mean the creation of depressed areas. The limitation of imports necessarily means the limitation of exports.
Belief in protectionism as a means of increasing the prosperity of the people of a country is the intellectual equivalent of the belief that 10-3=15.