You may think this photo is from a night shoot, but no. This is just after finishing our final scene on Day 5. There are a lot of reasons this one went long, not the least of which is that we were attempting the impossible--shooting actors on one boat from another boat without either boat being anchored to anything. What a nightmare. But even without that impossible task, we had a difficult time making our days, simply because everything takes longer than you expect. I don't know how many times I thought to myself that a particular simple scene or portion thereof would take a couple of hours when in fact it took two or three times that long. Learning to estimate the shooting schedule is critical, but coming to the realization that there is no such thing as a simple scene is a good start.
Even the simplest scene with two actors requires a minimum of 3-5 setups. Outside of the setup time required for blocking and lighting (30 to 90 minutes), there are a huge number of other factors which can eat time off the clock. Delays during setup can include power issues, equipment malfunctions, intermittent cloud cover, makeup and costume problems, missing props, location issues, crew indecision and more. Once you actually roll camera, there are any number of things that can ruin a take. These include actors missing marks, flubbing lines, looking at the camera or breaking continuity. Of course, you can expect multiple takes for getting the perfect performance as you have envisioned it. There are also camera issue such as lens flares, improper exposure, operator error, boom mic in shot, wrong framing, wrong timing between the dolly and actors, bugs or other stray objects in frame, or the biggest issue of all--missed focus. The sound department also contributes their share of re-takes for any number of sound issues including mic interference, visible mics, handling noise, air traffic, animals, insects, vehicles, trains, air conditioning units, lawn mowers, noisy off-screen cast and crew, and everything else you can imagine. Now, throw in complicated technical elements such as extras blocking, untrained animals, airplanes taking off/landing during a scene, remote-control helicopters hitting marks, etc.
This list is only things that happened during our recent film shoot to cause delays. It is by no means comprehensive. When you consider that a take must be free of all of these issues in order to be usable, it really does become necessary to shoot a huge number of takes in order to get even one that can be considered good. So, you can see why even a scene with only three setups (angles) can never be considered "simple." The lesson to be learned is that a shooting schedule with high per-day page counts will often result in either incomplete days or in compromised production value. Finding a balance between meeting the budget and keeping the quality high (technically and in performance) is certainly one of the biggest challenges a director faces.