The phrase 'What Has Been Seen Cannot Be Unseen' is a cornerstone of early internet culture, often used as a warning or reaction to disturbing, bizarre, or strangely captivating images. While its exact origin is difficult to pinpoint, it gained massive traction on imageboards like 4chan and Reddit during the mid-2000s, frequently paired with characters exhibiting wide-eyed shock, such as the O RLY owl or various wide-eyed anime expressions. The meme serves as a humorous acknowledgment of the psychological trauma of witnessing something unforgettable, leading to the popularization of 'eyebleach'—content meant to cleanse the mind after such an ordeal. Today, it remains a versatile tool for reacting to everything from cursed images to unexpected plot twists in pop culture.