Orwell's Animal Farm starts with a set of ideals that are set forth one night by a boar named Major. Unfortunately, Major dies three nights later.
Major's ideals, however, are picked up by the animals to which he had explained them and used as the springboard for a revolution in which the animals overthrow their human masters.
Unfortunately, as Orwell's novel progresses, we see that the pigs, who had been masterminds of the revolution, become corrupt and argue with one another. By the end of the novel, the pigs become allies of the humans whom Major had declared as enemies of the animals at the novel's outset.
Thus, Orwell seems to be predicting that over time the original ideals of a movement will become corrupted and forgotten. Thus, in the final lines of the novel, Orwell writes:
The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which.