Because books like "The Iliad" and "Shadows of Ecstasy" exist.
Homer is such a brilliant poet. I can hardly read certain chapters of "The Iliad" without getting caught up in the emotions of the world he depicts, foreign and even hostile as it is in comparison to ours. Isn't it perfectly absurd that I can both love AND hate Hektor, Achilleus, Odysseus and others? It's so easy to condemn them for their brutality: the apparent selfishness of their ends, the undeniable brutality of the means the utilize at times.
At the same time, there is something about their motives and misunderstandings and seeming helplessness before the gods which evokes a profound sympathy. It is a sympathy which can almost move me to admiration at times. The Achaians and Trojans are all mortal. Despite their godlikeness, there is still an insurmountable divide between the hero and the divine. The will of the gods and the decrees of fate can seem inescapable.
We know from the beginning of the book that Achilleus is fated to die in this war. We know that Troy will fall. We know that Sarpedon, the glorious son of Zeus, will be deliberately sacrificed by his father to achieve "higher ends". But the real heroes among mortals, despite their seeming weakness in the face of fate, don't just lie back and let their fate come to them. Agamemnon and many others lie back and blame their contentiousness or mistakes routinely on the "will of the gods". For the real heroes, this is not the only course, although the gods do have a role in things. Fate may be inescapable in the large scheme of things, but in the meantime, it can be met head on.
Sarpedon seems also to have some foreshadowing of his impending death - he meets it head on, however, saying effectively that although none of them is able to escape death, they can at least meet it with honour. Hektor will go out and fight for Troy even foreseeing its doom - he will even at times relapse into hope: perhaps this time, Troy's destruction might be forestalled. Achilleus is the best example of all. He, if any, has the opportunity to escape his fate. Rather, he has a "double fate": he could go home; he could die of old age, but live for all those years in obscurity. Through his anger and abandonment of the fight, this almost becomes his fate in fact. But with the death of Patroklos, he is awakened to a new sense of honour. This sense clearly indicates his duty to reenter the fight and the necessity of his acceptance of his alternate fate - the fate which will bring about his death in the war.
I don't have any clear ideas about the definite relationship between fate, the gods' wills and human choice. I guess that at the end of all this rambling my point is pretty simple. The heroism of these characters is, in my opinion, most clearly seen through their refusal to be caught in the dictatorship of fate. While no character is able to totally manipulate his own fate, while this fate is in some senses inescapable, the hero can to an extent determine how he will face this fate. Will he bow to it subserviently, or will he accept it boldly and with the truest manifestation of honour?
Hahaha... more questions! And they can't be conclusively answered! Gosh, do I love literature!