"Two rules are enough for the looks of a carpet; choose small figures [patterns] and avoid contrasts of colour. Small figures, however, have different meanings to different people. As a rule, a small figure is not more than three inches at most, at any way across. Very, very few rooms there are [that do not] look better with carpets of small design."
God forbid your carpet pattern be a hair over 3 inches across...
~ 'The Home Cook Book', 1877 (Hunter, Rose and Co, Toronto.)