The basic essence of which is the obstacle to a character's desire. How very important it is.
One panelist got into how important it was that the characters in conflict be in opposition. (I will add that this is even more important than that they desire strongly for conflict.)
Don't weasel out of the big scenes. If everything points to a big battle, give 'em a big battle. One panelist recounted having been on the way to New York to deliver the manuscript when her husband/co-author realized that the middle didn't work. They had 36 hours to tear it apart and give it a rewrite, with a big battle. But not flinching away and making life easy for your characters is crucial, especially with the big dramatic scenes.
One panelist observed that if you put Othello in Hamlet's place, the play would end in the first scene. I observed from the audience that in that case, Claudius would have known his character, and had guards, which he would have needed to weasel about -- like, say, feigning insanity and harmlessness. You can work with characters for conflict.