impermanence

Things in the world change in two ways. First, they change throughout time. Second, everything in this world is influenced by other elements of the world, and thus all existence is contingent upon something else. Because of this state of interdependence, everything that exists in this world is subject to change and is thus impermanent. Impermanence is the cause of suffering, because humans attempt to hold on to things that are constantly changing, on the mistaken assumption that those things are permanent.

(c) Encyclopedia of Buddhism, Impermanence