Yes, learning Rails is only a small part of learning Rails. That’s because… Learning Rails is not about learning Rails!
There are some mind-maps scattered across the Internet that try to explain why learning Ruby on Rails is hard. The main reason? It requires you to know a lot of different domains from databases, to design patterns, to…well, Rails itself.
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https://www.netguru.co/blog/why-learning-rails-is-not-so-hard