When I think of Ida, two literary touchstones come to mind, both of which have delighted me as a reader and inspired me as a writer. The first appears in the Greek myth of Oedipus. The young Oedipus, having heard a rumor that he is adopted, asks the Oracle at Delphi to identify his biological parents. Instead of answering his question, the Oracle replies that Oedipus is destined to kill his father and sleep with his mother—a bit off topic, yes, but interesting. What she doesn’t say is that his biological father is the King of Thebes, who cast out the newborn Oedipus precisely because she, the Oracle, prophesied long ago that the baby would someday kill the king. So it’s full disclosure all around...yet things go terribly wrong. True to form, the oracle’s advice is singularly unhelpful.
Then there are the trio of witches that the warrior MacBeth meets on his way home from battle. They let it slip that he will soon replace Duncan as the King of Scotland—an event MacBeth hastens along with a knife. When he frets about being caught, MacBeth checks in with the witches again, and this time they share the idea that he can’t be killed until the forest at Birnham Wood comes to Dunsinane Hill—which, given the rate at which forests travel, MacBeth assumes won’t happen for some time. Knowing one is invincible gives one quite a lot of courage, he discovers. But despite the witches’ predictions, things once again go terribly wrong. From this we conclude that MacBeth slept through his English classes when they studied Oedipus Rex.
One last stray thought: You could make the argument that Ida is in some sense Edgar’s opposite. She speaks without understanding what she means, while Edgar understands things about which he cannot speak. That accounts, at least in part, for their mutual fascination.