“Which man is bigger? It seems like there should be an easy answer, but when you compare the two men on each dimension, the answer turns out to be more elusive than we might expect. The man on the right is tall but has narrow shoulders. The man on the left has a large waist but nearly average-size hips. You might attempt to determine which man is bigger by simply taking the average of all nine of each man’s dimensions—except... you would discover that each man’s average size is nearly identical. At the same time, we can see that it would be misleading to say they are the same size—or to describe either one of them as average: the man on the left is average on two dimensions (reach and chest), while the man on the right is barely average on only one dimension (waist). There is no simple answer to the question, ‘Which man is bigger?’
...[This] reveals an important truth about human beings and the first principle of individuality: the jaggedness principle. This principle holds that we cannot apply one-dimensional thinking to understand something that is complex and ‘jagged’... A quality is jagged if it meets two criteria. First, it must consist of multiple dimensions. Second, these dimensions must be weakly related to one another. Jaggedness is not just about human size; almost every human characteristic that we care about—including talent, intelligence, character, creativity... is jagged.
[...] Height is one-dimensional, so it is perfectly acceptable to rank people according to how tall they are. But human size is a different story: it is composed of many different dimensions that are not strongly linked... if we were to expand the average band to include the middle 90 percent of each dimension, instead of the middle 30 percent... You might guess that most people’s bodies would surely lie within such a wide range. In actuality, less than half of all people would.20 It turns out that most of us have at least one body part that is rather large or rather small. That is why a cockpit designed for the average is a cockpit designed for nobody.
...[I]gnoring the multidimensionality of size is never a good compromise. When it matters, there are no shortcuts: you can only produce a good fit if you think about size in terms of all its dimensions.”
— Todd Rose, The End of Average