Walter Richard Miles

"From the standpoint of a science that seeks expression in universal generalizations our knowledge of human behavior seems to be seriously handicapped by two kinds of variability. In the first place, no two persons react in exactly the same way to identical stimuli; and in the second place, the individual does not always react similarly to the same stimulus. Individual differences in the so-called personal equation delayed the beginnings of a science of human nature for a long time. It was a fruitful technical advance when psychology rescued individual differences from the scrap-heap of scientific anomalies and began to study them. At the present time surfaces of frequency and the relative position of individuals in a distribution of individual differences expresses our knowledge of human nature vastly better than the hypothetical 'average man' of a few years ago"--Preface. (PsycINFO Database Record (c) 2010 APA, all rights reserved).

Books like Psychological Studies of Human Variability

Your next favorite book is out there