It "is curious to observe how the nature of truth may be changed by the garb it wears; softened to the admonition of friendship, or soured into the severity of reproof: yet this severity may be useful to some tempers; it somewhat resembles a file; disagreeable in its operation, but hard metals may be the brighter for it."
— Mackenzie, Henry (1745-1831)
(p. 33 in Oxford edition)
See The Man of Feeling (London: Printed for T. Cadell, in the Strand, 1771). <Link to ECCO>
Reading Henry Mackenzie, The Man of Feeling, ed. Brian Vickers. (Oxford: Oxford UP, 2001).