Sustainable software development is best summarized by Robert Redford in the movie Spy Game: Technology gets better everyday. That's fine. But most of the time all you need is a stick of gum, a pocket knife and a smile.Frameworks become more intuitive. Platforms become more performant. Programming languages become more expressive. All of this is relevant, but pales in comparison to understanding the underlying principles regarding why and how all of these improvements have been made. Recognizing this fact helps us produce maintainable systems and avoid career dead ends.