1. The page may be extinct, like many whales, chimpanzees, and gorillas in the wild could be without your help.
2. The page may have moved, like many Pacific Islanders will have to do when their homes sink beneath the waves due to global warming.
3. You may have made a mistake typing the address, or we made a mistake creating a link. Mistakes happen. Chernobyl and Bhopal should have taught us that they can have devastating consequences, which is why releasing inadequately tested genetically engineered crops into nature is stupid and dangerous.
4. Our web server may be malfunctioning. This happens to large complicated technical systems often, which is why the Star Wars missile defense system will never work and shouldn't be deployed.
Roland Savery painted this image of a live Dodo, which was brought to Europe in the early 17 century