From Adam Green’s The second coming of the Web:

“When Tim Berners-Lee first gave mankind the Web, he made a tragic mistake. He granted us free will to use less than perfect HTML. His tools, and the tools of those to follow him, allowed users to develop sinful habits based on ignorance and sloth. The result was a Web of corrupt data, in which misformed tags abounded. This great fall from grace by the users of the Web prevented it from ever attaining the state of perfection desired by all computer scientists, a completely machine readable database.”