Acting is a skill. Acting is an art. Actors can have genius in them. But actors often don't have to see beyond the lines they're given, beyond the role they're playing in any given scene. Actors can afford to have tunnel vision. But the director, the director has to be able to keep an entire movie in their head at all times. They have to be able to execute the smallest details of scene - let's move that lamp to the other side of the bed in the opening scene - while simultaneously seeing how that decision might effect the entirety of the movie - in the closing scene, when he darts out of bed to confront the robber, he should knock that lamp over.