Tony Zhou of Every Frame A Painting does a wonderful job explaining something that can't quite be explained except with proper examples. That is, how does an editor know when to cut in a film? How does he know when to cut? Well, it helps first to have a ton of great directors to follow after, but in the end, it really just comes down to practice. You cut here, you cut there, and you gauge how an audience responds to a cut. Did it propel the film forward and support the characters' emotions in the scene? Does it help to tell the story? Does the cut make the emotion feel real?