Struggle.

"First of all, you have heard me talk of Logres. It was the old name for this country, thousands of years ago; in the old days when the struggle between good and evil was more bitter and open than it is now. That struggle goes on all around us all the time, like two armies fighting. And sometimes one of them seems to be winning and sometimes the other, but neither has ever triumphed altogether. Nor ever will," he added softly to himself, "for there is something of each in every man."

-Susan Cooper

-Chapter VI, Over Sea, Under Stone

Lessons from the Geese.

"Will you stop about it at once! What a horrible mind you must have! You have no right to say such things. And of course there are sentries. There are the jer-falcons and the peregrines, aren't there: the foxes and the ermines and the humans with their nets? These are natural enemies. But what creature could be so low as to go about in bands, to murder others of its own blood?"

-T. H. White 

Part I, Chapter XIX, The Once and Future King