A rule about the control of variability is reducing expectation of reward increases variation of the form of rewarded actions. This is a rule about how food-getting knowledge is gathered, something we know almost nothing about. Almost all instrumental learning experiments are about how food-getting knowledge is used. Not only do we know almost nothing about how such knowledge is gathered, the question is almost never studied. Similar gaps exist in the study of human learning and economics. In human learning, how the environment controls curiosity is never studied. Likewise,  economics theories are almost entirely about how people use economically-valuable knowledge. How the environment controls creation of that knowledge is a mystery that textbooks and researchers ignore.