Rails is the only environment in which I've routinely found myself utterly stumped. Not because it's hard, because it isn't. But the thick layer of "magic" makes it awfully hard to debug sometimes.
It's also dangerous because Rails fits a specific niche, like he mentions--building (potentially) many web systems quickly. We chose to migrate large legacy systems to rails, which meant lots of the nice convention just. doesn't. work. Day 1, you're already digging in to figure out how to get around the magic!
That's why I'm excited about Sean Griffin's work on the [Attributes API](http://edgeapi.rubyonrails.org/classes/ActiveRecord/Attribut...). To do it, he's had to refactor out a lot of internal monkey patching so that (in Rails 5) there is only one source of type information for an AR model. This means gems can extend AR, I can extend AR, new requirements can walk into my door that I can deliver on without monkey patching or opening Pandora's box of a patch of crappy Rails internals. The magic is still there, but it's done it a way so the magic doesn't fall apart in unexpected, unmanageable ways. That's what matters to me.