Beginning in medias res fosters dramatization from the first line for the writer. When you're busy displaying the scene as it happens, you won't have much time to talk about the characters or the circumstances. When using this strategy, you may need to fill in some background information at some point. But for now, readers can understand more fully what's going on by seeing and hearing it firsthand. The ancient Greek playwrights began their poems in medias res because there were no costumes, only body paint that was worn away by sweat and blood. So the first thing they needed to show the audience was scenery. They did this by describing a location either exactly or vaguely enough to make everyone think it was somewhere else. For example, one poet might describe a beach with waves crashing against a rocky shoreline, while another might say only that his location was near a river. Today, writers still sometimes start their novels in medias res for the same reason as the ancient Greeks--because there are certain scenes that cannot be explained or revealed through dialogue alone. For example, if a character gets stabbed, you wouldn't want to wait until later in the story to reveal where it happened or who did it. You would simply show us the scene in all of its bloody glory from the beginning. In addition to helping writers avoid explaining things that shouldn't be said out loud, starting in medias res also lets them explore other possibilities with less restriction.