The largest part of the primate prefrontal cortex has no homolog in other mammals. Accordingly, it probably confers some advantage that other mammals either lack or attain through the function of other structures. Yet, this advantage remains enigmatic. This is not so for other parts of the cortex. For example, certain visual areas encode, represent and store knowledge about objects. By analogy, perhaps the primate prefrontal cortex encodes, represents and stores knowledge about behaviors, including the consequences of doing (or not doing) something in complex and challenging situations. The long list of functions often attributed to the prefrontal cortex could contribute to knowing what to do and what will happen when rare risks arise or outstanding opportunities knock.