I've been learning Ruby and Rails primarily through contributing to Discourse (the software that is running this platform). The biggest holdups I've had to date have been probably some assumptions I have from other languages like C# and that really do not work the same in Ruby. Such as Class inheritance, Extending Classes, and the fact that a lot of magic still happens behind the scenes in Ruby, such as, routing calling out to its controllers, and the controllers interacting with their models.
Does your book provide any insight to some of that magic? I've gone through Code Academy's course, and a couple at Treehouse, but that was 2 years ago and I feel like I am constantly forgetting that knowledge (primarily because I'm only in Ruby/Rails for a limited time, then back to full time in C#).