Once upon a time...
It all started in September 2013. Having just returned from the first European Ember.js conference, my enthusiasm went through the roof. I wanted to spread the word, for people to realize how beautiful Ember is, for them to know that Ember.js is not that hard to learn. It's just a matter of having the core concepts internalized.
So without proper equipment (and after a few episodes, with a ~$80 mic) I started producing screencasts, a series in which a simple application is developed step-by-step. I sent the first few to my subscribers and kept producing them. And people seemed to have liked them.
Once the screencast series was finished, I switched to blog posts and lengthier articles, and in 2014 I committed to posting something of value each week. Then, after a long labor of (mostly) love, I published the 1st edition of the book in Feburary 2015, that used the then stable Ember version, 1.10.
I was not done, though. As Ember made progress in a neck breaking pace, I kept the book up-to-date with the actual stable version of the framework, and adding material that covered the new features.
Version 2 of the book, that is running on Ember 2, was published about 6 months later and I've been updating the book for every minor version ever since.