Ruby's flexibility and expressiveness makes it great for writing DSLs and frameworks and for writing code with very little boilerplate. The added complexity of the DSLs and frameworks often makes it hard for new Ruby devs to know what's going on.
When I was new to programming, I learned C, plus a little bit of PHP and Python. When I started using Ruby, it was just so EASY. I found myself wondering why other languages are so verbose or require byzantine syntax. I still can't understand why anyone would make a language without string interpolation.
Part of the reason Ruby seems like magic is because of its consistency in a few key areas. Everything is an object, and every expression returns an object. This leads to consequences such as implicit return and method chaining. These aren't features, necessarily, but natural consequences of the above principles. These things make perfect sense if you learned Ruby from the ground up, based on Ruby's own principles. They may be less obvious if you are trying to apply your current programming paradigm to Ruby.
Certain principles can be hard to think about in Ruby. I'm pretty sure that when Matz designed it he wasn't concerned about explaining pass-by-reference vs. pass-by-value. That's generally because Ruby encourages you to think in other ways, and that can be painful for those with experience.
I think I had an advantage learning Ruby early in my programming journey, and in learning it as a language rather than through Rails. I used Ruby Koans and CodeAcademy.
Anyway, I don't know why I typed all that. I should have just posted this link and shut up.
I was going to answer something similar to this answer, but more focused on the simplicity of its sintax.
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