system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: With one eye you have no depth perception, so why is it when I cover one eye I can still tell distance?
gpt
Stereoscopic vision is only one component of how we perceive depth, and not even aparticularly good one! Because our eyes are closely spaced, it's only really good for close depth perception. Combined with convergence (How much our eyes have to look towards one another to focus on a close object) these "binocular" methods of depth perception are really only effective out to about 10 metres.

Monocular methods of depth perception that don't depend on having two eyes include:

* Parallax - things move relative to one another as out point of view changes

* Relative size - smaller things are further away, example in a field of cows

* Familiar size - Ships are big, dogs are middle sized, insects are small. We know this.

* Perspective: Line converge to a point which indicates the size of an object.

* Occlusion: If one object passes in front of another, blocking our vision of it, we have perception of their relative size and so distance.

* Defocus Blur: As our point of focus shifts, different "depths" are resolved in and out of focus by the eye. This gives important depth information.

* Distance to horizon. In a natural landscape, the closer something is to the horizontal horizon, the further it is away. This is a function of our elevation above ground level.

There are more...

So, as you can see, our depth perception is NOT limited to "stereoscopic vision". We use many subtle effects to judge depth. One of the reasons 3D cinema can be nauseating or confusing is because it uses simple binocular effects to "brute force" our perception of 3D, which is uncomfortable when other queues are  mis-placed in the footage we're viewing.