Every time I am forced to work with XML, I wonder how differently it would have turned out had 10% of the resources devoted to building increasingly complex and tangled specs had been instead directed towards making tools and documentation which aren’t terrible. Little things like the user-hostile APIs for namespaces, validation, extension, etc. and often horrible error messages, not to mention the lack of updates for common open source libraries like libxml2 really cemented the XML=pain reputation by the time JSON came along.