Let us start from the experience of divine temptation or infatuation (até) which led Agamemnon to compensate himself for the loss of his own mistress by robbing Achilles of his. "Not I," he declared afterwards, "not I was the cause of this act, but Zeus and my portion and the Erinys who walks in darkness: they it [were] who in the assembly put wild ate in my understanding, on that day when I arbitrarily took Achilles prize from him> So what could I do? Deity will always have its way." By impatient modern readers these words of Agamemnon have sometimes been dismissed as a weak excuse or evasion of responsibility. But not, I think, by those who read carefully. An evasion of responsibility in the juridical sense these words certainly are not; for at the end of his speech Agamemnon offers compensation precisely on this ground -- "But since I was blinded by ate and Zeus took awsay my understanding, I am willing to make my peace and give abundant compensation." Had he acted of his own volition, he could not so easily admit himself in the wrong; as it is, he will pay for his acts. (Pages 2-3)

At this point, the reader may naturally ask whether we are dealing with anything more than a [traditional expression]. ... [however,] even a [traditional expression] must have an origin. It may help us .. if we look a little more closely at the nature of ate and of the agencies to which Agamemnon ascribes it, and then glance at some other sorts of statement which the epic poets make about the sources of human behavior.
Always, or practically always, ate is a state of mind -- a temporary clouding or bewildering of the normal consciousness. It is, in fact, a partial and temporary insanity; and, like all insanity, it is ascribed not to physiologial or psychological causes, but to external "daemonic" agency. (Pages 4-5)

A word next about the agencies to which ate is ascribed. Agamemnon cites not one such agency, but three: Zeus and moira and the Erinys who walks in darkness... Moira, I think, is brought in because people spoke of any unaccountable personal disaster as part of their "portion" or "lot," meaning simply that they cannot understand why it happened, but since it has happened, evidently "it had to be." ... by blaming his moira, Agamemnon no more declares himself a systematic determinist than does the modern Greek peasant when he uses similar language. To ask whether Homer's people are determinists or libertarians is a fantastic anachronism: the question has never occurred to them... What they do recognize is the distinction between normal actions and actions performed in a state of ate. (Pages 6-7)

Whenever someone has a particularly brilliant or a particularly foolish idea; when he suddenly recognises another person's identity or sees in a flash the meaning of an omen; when he remembers what he might well have forgotten or forgets what he should have remembered, he or someone else will see in it, if we are to take the words literally, a psychic intervention by [a "god" or "gods."] Doubtless, they do not always expect to be taken literally .. And indeed that is how we should expect people to talk who believed (or whose ancestors believed) in daily and hourly monitions. The recognition, the insight, the memory, the brilliant or perverse idea, have this in common, that they come suddenly, as we may say, "into a man's head." Often he is conscious of no observation or reasoning which has led up to them. But in that case, how can he call them "his"? A moment ago they were not in his mind; now they are there. Something has put them there and that something is other than himself. More than this he does not know. So he speaks of it noncommittally as "the gods" or "some god" ... (page 11)

We may sum up the result by saying that all departures from normal human behavior whose causes are not immediately perceived, whether by the subjects' own consciousness or by the observations of others, are ascribed to supernatural agency, just as is any departure from the normal behavior of the weather or the normal behavior of a bowstring. ... And I suggest that in general the inward monition, or the sudden unaccountable feeling of power, or the sudden unaccountable loss of judgement, is the germ out of which the divine machinery developed. (pages 13-14)

From "Agamemnon's Apology," Chapter I, E. R. Dodds, The Greeks and the Irrational University of California Press: Berkeley and Los Angeles, CA, 1951.