tl;dr:“We have spent most of the last couple of decades helping large organizations overhaul their legacy systems. In doing this we've learned a great deal about what works and seen many paths that lead to failure. We've decided to set aside some time to writing down what we've learned in the form of various patterns that we've seen used.” The authors believe the following four activities should be done in sequence: (1) Understand the outcomes you want to achieve. (2) Decide how to break the problem up into smaller parts. (3) Successfully deliver the parts. (4) Change the organization to allow this to happen on an ongoing basis.