Systems Architecture - What do I need that for

When the architecture is an artefact of the passt how are you supposed to make a good descision

“What do I need that for?”

That is the number one question I get after a meeting updating the architecture with a function owner. How do you answer that question? The architecture already exists in their head, is written down somewhere else, the function is already being built, and many decisions have already been made. We just finished the first session—one of many—and the first thought of the function owner was: What do I need that for?

How do you answer this question? The go-to response is usually: “We need to keep the system architecture up to date.” While this is true, it takes responsibility away from the function owner. Additionally, the function owner is asking what they need it for, which implies they don’t see any value in a shared system architecture. So how do you answer a question when the other person doesn’t see the value? The go-to answer actually confirms what the function owner implies: there is no direct value for them.

If the function owner asks this question, we have to assume that they already have an architecture in their head or written down somewhere else—not in the shared system architecture. Otherwise, the question would never cross their mind in the first place.

If we take a step back and ask ourselves why we create a system architecture, the answer is simple: to provide every discipline with a shared foundation for making decisions.

So, what does it mean when we update the architecture together with a function owner? By updating the system architecture, we add new information to it, making it the single source of truth. Instead of giving the academic, go-to answer, we should explain that the function owner needs the architecture for their next decision.

More importantly, they are not updating it just for themselves—they are updating it for every other function owner who needs to make decisions that align with the rest of the system. Furthermore, updating the architecture often reveals information the current function owner hadn’t considered. Looking beyond the boundaries of their own function and into the surrounding system often exposes gaps, dependencies, or assumptions that would otherwise remain hidden.

The function owner who asks, “What do I need that for?” is treating the architecture as a record of the past. By updating the architecture, the architecture grows together with the system.

Every decision changes the system. Every change should update the architecture. Otherwise, the next engineer is making decisions based on yesterday’s understanding. When the architecture can no longer be trusted, everyone starts building their own version of the system – whether it’s in their head, on a whiteboard, or in a spreadsheet. Function owners do not suddenly stop making decisions; they simply stop making them together. That is the moment the single source of truth stops being singular.

So our answer to the question:

“What do I need this for?”,

should never be:

“Because it’s part of the process”.

Our answer should be:

“Because someone else’s next decision depends on yours. And you never know what you didn’t think about until the architecture shows you.”