Film is the art of faking reality. Here's a simple example. We have a shot where the main viewscreen flares white for a few frames, but during principle photography no shots were made with bright light coming from behind the screen. To sell the flash, I created a matte of the main viewscreen glow and the light it would cast on the wall and handrails so that I could selectively brighten parts of the image and not others. This affects maybe three frames total, but it sells the illusion.