… is from page 653 of the 1988 collection of Lord Acton’s writings (edited by the late J. Rufus Fears), Essays in Religion, Politics, and Morality; specifically, it’s from Acton’s letter of June 1st, 1880, to Mary Gladstone (ellipses and brackets original to J. Rufus Fears):
The great intellectual and moral defect of the present day … [is] the habit of dwelling on appearances, not on realities….
DBx: And so this same intellectual and moral defect continues more than 140 years later.