The central plot element of the Oresteia by Aeschylus is the cycle of vengance bred from the curse in the house of Atreus. The chorus states:
But blood of man once spilled,
Once at his feet shed forth, and darkening the plain,-
Nor chant nor charm can call it back again.
So Zeus hath willed...
Thus in the play there is no way that the participants can escape the curse until the Furies are transformed to the Eumenides. Agamemnon is required to sacrifice Iphegenia to appease the angry Artemis, which starts to cycle of Clytemnestra's killing Agammenon and then Orestes' killing Clytemnestra. Even Cassandra, though she can actually foresee the events about to happen is cursed with not being believed and thus cannot forestall them. This issue of the inability of mortals to escape destiny is repeated emphasized in the choral odes. In the actual Greek, one gets an almost eerie repetition of the word "dikê" (justice) and similar sounding words