This document provides a summary and conclusions from a lecture on enterprise application architecture. It discusses that building complex computer systems gets exponentially harder with increased complexity. However, with proper techniques like layering, interfaces, object-oriented programming, design patterns, and frameworks, building large multi-tier systems can be done incrementally. It emphasizes separating concerns, minimizing dependencies between layers, and avoiding unnecessary complexity. Practical considerations include avoiding overdesign, overconfiguration, and not being constrained by frameworks. The future of enterprise software will involve challenges of connectivity between an increasing number of devices and software integration through APIs, cloud computing, and mobility.