Let's consider four categories of fit between people and prod- ucts. The first is physical-the interaction of our bones, muscles, hearts, and lungs with built objects. The second is concerned with the senses-vision, touch, smell, and so on. The third is cognitive the mind-machine interaction. Fourth, we will talk about problems resulting from system complexity. Each category demonstrates different aspects of the problem of fit, and each has its own wisdom necessary for the designer of good products.
— Good products, bad products by James Adams (Page 70)
This is the first observation of the book that made me sit up and say, "Yes, that's insightful."