You probably have been there before. You visit a website and instead of the content, a 404 error shows up saying that the page is not available. A 404 error can be the result of various reasons. The main reason is when the content of a website has been removed or moved to another URL without a proper redirection. The other reason can be that you typed the URL wrong. Generally, 404 errors are bad for user experience and should be fixed as soon as possible.