The only thing that is constant is change. Most of the time, changes mean evolving. Operating systems keep changing with new versions and upgrades, while frameworks and libraries keep changing with new releases. Applications keep changing with new versions. Those that do not change are the systems that either are not being actively used or are abandoned. Changes are inevitable.

Making plans is to keep things organized. And it takes an effort to build a plan. However, the following one doesn't mean you must not change it when a change is really needed. Sticking to a plan that is no longer heading in the right direction will either end in failure or will require much greater efforts to get it back on track later.

Due to the scope of this book, we're not going to discuss the twelve principles in the Agile manifesto. If you're interested to learn more about Agile, I recommend the book Learning Agile, by Andrew Stellman and Jennifer Greene. It's a must-read for Agile practitioners. Another interesting book is Succeeding with Agile: Software Development Using Scrum, by Mike Cohn, which is a guide to starting Agile with Scrum.