… is from page 172 of volume 1 of The Collected Works of James M. Buchanan: The Logical Foundations of Constitutional Liberty; specifically, it’s from Jim’s 1987 essay “Keynesian Follies”:
The Keynesian intellectual “fog,” for that is what the whole discussion surely reflected, was motivated, in part, by the underlying purpose of securing widespread public and political acceptance of an activist fiscal policy regime. To convince the noneconomist public to abandon the classical precepts of fiscal prudence, the Keynesians felt that they needed to show that public debt did not matter because, after all, “we owe it to ourselves.”
Jim’s first book – Public Principles of Public Debt (1958) – exposed the folly of the notion that internally held public debt, because it is owed “to ourselves,” is not a burden.