If there was ever a real mystery attached to film-making, it probably belonged to the same mythical era as the Golden Age stars: when fans watched in awe and wonderment rather than with cynicism and scrutiny at the top of their agenda. It was the veil held up to protect fans from seeing how the tricks were achieved, but as fandom became more voracious and knowledge of process became the great currency of Internet fans, it's gone.
Now, intrigue has replaced it: fans want to have the curtain peeled back. They want to see how iconic special effects sequences were shot; how directors achieved their most mysterious, magical moments, and how production directly feeds into product. We're obsessive compulsive mystery ruiners, and unfortunately, looking too hard can completely spoil the magic of the films.
Like curiosity killing the cat, seeing some behind-the-scenes shots from iconic movies can completely ruin your enjoyment of key scenes in them.