Canadian astronaut Chris Hadfield has repeatedly addressed the myth directly, explaining that from low Earth orbit you cannot pick out the Great Wall of China with unaided human vision. The reason is not its length but its narrow width and low contrast against surrounding terrain, which makes it fall below practical naked-eye resolution at orbital distances.
This matches the broader evidence base cited in major references. NASA states that, despite the myth, the Wall is “difficult or impossible to see from Earth orbit” without high-powered lenses, and peer-reviewed optical analyses (e.g., a review hosted on PMC) conclude that even very good eyesight would not reliably detect it at a glance from space because of human visual-acuity limits relative to the Wall’s meter-scale width.
Reports from Chinese scientific and astronaut sources also reinforce this consensus: coverage citing analyses by researchers at the Chinese Academy of Sciences’ Institute of Optics and Electronics and statements attributed to China’s first astronaut Yang Liwei report that he could not see the Great Wall from space. Together, these sources explain why occasional anecdotal claims do not outweigh quantified optical limits and repeated astronaut testimony.