According to David Heinemeier Hansson, you will never understand it all. Case in point? David himself.
That was the gist of his answer to how a new change to the way rails 3 renders actions in the browser would be handled for older browsers.
DHH gets involved in the parts he cares about and doesn’t worry about the exact details that have been delegated to someone else. He says we should not worry about knowing the whole framework because he doesn’t either. We don’t need to live up to an impossible standard.