many elements in the system and each can be in one of a large number of states, then figuring out what is going on and what you should do about it grows impossible. • Interdependencies. When each element in the system can affect each other element in unpredictable ways, it's easy to induce harmonics and other non-linear responses, driving the system out of control. • Uncertainty. When outside stresses on the system are unpredictable, the system never settles down to an equilibrium. • Irreversibility. When the effects of decisions can't be predicted and they can't be easily undone, decisions grow prohibitively expensive. Taming Complexity with Reversibility — Kent Beck