A student's canvas has a large pale mass just left of centre and feels as though it is sliding off the left edge. She proposes to shrink the mass. Why is adding a small dark accent near the right edge usually the better repair?

D. Weight acts by distance from centre; a distant mark adds leverage without altering the mass.

Distance multiplies. An accent at the edge sits four or five times further out than the mass, so a fraction of its weight supplies the same moment, and the passage the student already likes is left alone. Shrinking the mass changes weight and distance together and usually costs the picture its subject.