" Rule number three: only three may play. No more, no less. Three. A number favored as much by art as by science: primary colors, points required to locate an object in space, notes to form a musical chord. Three points of a triangle, the first geometrical figure. Incontrovertible fact: two straight lines cannot enclose a space. The points of a triangle may move, shift allegiance, the distance between two disappear as they draw away from the third, but together they always define a triangle. Self-contained, real, complete. "

― Kate Morton , The House at Riverton