Building with loosely coupled parts
Large, complex software projects tend to collapse under the weight of administration. No single developer can understand the entire system that they’re contributing to, yet each new member added to a project team increases the complexity of the entire team’s interactions, necessitating new supervisory roles like “software architects,” with whom developers must check before doing any work. The contributors need to coordinate carefully to avoid conflict between their efforts. As a team grows, they’re forced to spend increasing amounts of time managing the project, and decreasing amounts of time actually doing the work.
To avoid this fate, it’s smarter to break large projects into a handful of small, quasi-independent software projects. In this model, each component communicates with other components through simple, modular standards, so that any one piece can be swapped out at any time. Instead of building a monolith that everybody will lament in a few years, you build a little ecosystem, in which each piece can be upgraded and modified easily, as changing needs will demand. Each component is maintained by a single agile team, which documents the component’s application programming interface (API) — the grammatical rules that other components can use to communicate with it. The teams’ need to coordinate is minimal, because they can simply follow the API documentation for the other components that they need to interface with.
When each component uses abstracted APIs (think of them as common standards for using that technology), this is known as using "service-oriented architecture" (SOA). This is the same as the concept of "interchangeable parts" that made the industrial revolution possible. Standardized couplings are the underlying concept behind cloud computing, electrical outlets, USB, Legos, trains, and countless other modern products and practices.
Building IT systems using loosely coupled parts, connected by open and available APIs, is the "magic bullet" that allows for flexible, sustainable systems that meet user needs and cost less over time.