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One is apt to overestimate beauty when it is rare

Mark Twain (1869). “The Innocents Abroad, Or, The New Pilgrims' Progress: Being Some Account of the Steamship Quaker City's Pleasure Excursion to Europe and the Holy Land : with Descriptions of Countries, Nations, Incidents, and Adventures as They Appeared to the Author”, p.546
One is apt to overestimate beauty when it is rare