Why is it so hard to separate myth from fact around Ancient Greece period?

The Greeks considered Homer to be the first poet of the Hellens and the greatest. Hesiod even came in a relatively distant second to Homer’s popularity. His two works the Iliad and the Odyssey are not the only poems in this heroic cycle, but they are the two most complete. For the rest, we only have fragments. They do give us some of our best glimpses at this age in Greek history. Your follow up question for the week: Why is it so hard to separate myth from fact around this period?