An idea going back to Plato's Meno is that knowledge is stable. Recently, a seemingly stronger and more exciting thesis has been advanced, namely that rational belief is stable. I sketch two recent stability theories of knowledge and belief, and present an example intended to show that knowledge need not be stable and belief need not be stable either. The second claim does not follow from the first, even though we take knowledge to be a special kind of belief. "Stability" is an ambiguous term that may refer to stability under reflection or to stability under updating.