From the design test I recently posted, here is the first answer directly from the book..
The left side is the better design because it is more unified than the right, and at the same time it has as much variety, On the left side there are more contrasting values with the black preponderant. There is a contrast of line with curved lines dominant. There are contrasting directions with the vertical dominating. The left is also more interesting than the right because of a variety of spacing, that is, the three vertical lines are not monotonously spaced as are the lines in the right side design, but have large and small spaces between them. The right side is structurally weak. There are contrasting values, lines. and directions, none of which dominates.