The idea that certain devices or contraptions are inherently "magic" in some way and mere mortals are incapable of understanding their inner-workings. Some devices subject to "magic box theory" are (but are not limited to) computers, car engines/transmissions, microwaves, televisions, radios, calculators, etc.
Believers of the magic box theory are easily singled out by judging the reaction after giving them a simple request such as "open your hood" or "open the side of your computer".
A commonly held belief among Magic Box Theorists is that these devices have a will of their own with some sort of propensity toward a specific behavior. They can be heard stating that their "computer is acting funny" or that their "car is behaving differently", completely oblivious to the fact that computers and cars do not behave, they are behaved upon.
I told my boss's wife I could fix her computer. She said that's impossible because something is wrong with the "inside parts". Apparently she is a "Magic Box Theorist".
My boss wasn't sure if his car had antifreeze for the winter so I told him to open his hood and check. He freaked out and nearly choked to death on his tea. He, like his wife, subscribes to the "Magic Box Theory"
My friend's dad got a new TV and I set it up. A few days later he calls me and says "I pressed some button on the remote and now the TV isn't acting right". I'm sure that may have something to do with what action was taken on the TV e.g., the remote. Apparently, my friend's dad is a "Magic Box Theorist"