Wow… This is the best article about software I’ve read in a long time! I’m very much in the same boat as you were — I understand separation of concerns as a concept, but have no idea how to apply it. I also didn’t know how closely this practice related to success in building apps. This article has really sold me on finally taking the plunge, eating the time lost to the learning curve, and finally forcing myself to do TDD. Thanks for writing it!