system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does the Nintendo 3DS work?

How does the 3DS display 3D gameplay with just turning the switch on?
gpt
The screen is displaying two images at once, in alternating vertical columns.  In front of the screen is a barrier that blocks half of the columns.  When you're at the right distance away from the screen, the barrier blocks one image entirely for one eye, and the other for the other eye, creating a 3D effect.  At the wrong distance, you get a garbled mess of both images.  Turning the effect off just causes the entire screen to display the same image.  The barrier is still there, but now it doesn't matter what angle you view it from, both eyes will see the same image.