In this work, I investigate what power-law processes may have in common. I propose that their common feature is a specific type of positive feedback. Next, I discuss two specific power-law models for processes which appear to be quite different from one another: (1) citations of scientific papers, and (2) physical interactions between proteins in cells. Finally, I discuss a new theoretical framework for describing power-law phenomena, based on the principle of maximum entropy, combined with a symmetry relationship.