A Matter of Balance

I examined a scattered row of wooden domino tiles on the table. Each tile is precisely twice as long as it is wide. I paused, calculating the spacing, then gripped one by the edge with my clip hands. Carefully, I placed three upright, spaced by exactly half a tile's length, forming a miniature gateway. A small vibration from a nearby clock shook the surface slightly. Instead of knocking them over, I adjusted the angle of the left upright by two millimeters. The structure held firm. Perfect symmetry achieved.