Magento’s choice of configuration (via XML) over convention is part of what makes the system so awesomely flexible and extensible. The downside is that it also has a tendency to lead to those ‘WTF’ moments when you know you’ve done *something* wrong, but you have no idea *what*.
Having some background on Magento’s routing system is super helpful in the situation where you’ve created a controller and a route, but for some reason your controller is not being used and you’re getting an unhelpful 404 page instead of whatever functionality you’re expecting. The meat of the code that handles request routing in Magento can be found at ./app/code/core/Mage/Core/Controller/Varien/Router/
In the case above, it can be useful to refer to the standard router in Standard.php, specifically the match() method. This contains the bulk of the logic that tries to match a URL to a module, controller, and action. You can dump or inspect the contents of $this->_modules, or just the local $modules, to view the modules Magento has registered, and $p to see how Magento has broken the URL parts up.
It can also be helpful to dump and do a search on the global config object – I wrote a super simple free extension to do just that.