system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are two-way mirrors called TWO-way mirrors if the entire purpose of them is that they only let you see through them in one direction?
gpt
They are sometimes called two way mirrors, because in truth you can see through either side, what matters is which side is brighter and which side is darker in terms of lighting. The dark side can see through to the bright side, but not the reverse. 

These mirrors are referred to as both two-way and one-way mirrors, confusingly.