Ruby's metaprogramming allows you to create really nice, ergonomic abstractions. I can write `has_one :posts` in a User model class in Rails and a ton of useful functionality pops into existence.

On the other hand, that deep magic metaprogramming can be really hard to follow if you need to understand how it works. Tracing back through (or even debugging) a metaprogramming-heavy codebase is a nightmare.

I'd argue that deep magic metaprogramming is great for when you have abstractions you almost never need to dig into. Rails is great because it's relatively rare that I need to go spelunking in the rails codebase itself (and thus understand the deep magic). Instead, I can rely on a huge pile of documentation, stack overflow answers, conference talks, etc to figure out how to use rails' abstractions (like `has_one :posts`) without needing to understand their implementation.

On the other hand, the average production codebase should minimize their use of metaprogramming. When I don't understand how Joe's `Whatsit` interface works, I'm much more likely to need to dig into Joe's code to understand how to use that abstraction. If I have to understand Joe's deep magic every time I do that, it's a net loss.