The Same Mistakes Happen in the Same Domain Repeatedly

Post-mortems and retrospectives show the same root causes appearing in the same areas. Each new team makes decisions that previous teams already tried and abandoned.
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  2 minute read  

What you are seeing

A post-mortem reveals that the payments module failed in the same way it failed eighteen months ago. The fix applied then was not documented, and the developer who applied it is no longer on the team. A retrospective surfaces a proposal to split the monolith into services - a direction the team two rotations ago evaluated and rejected for reasons nobody on the current team knows.

The same conversations happen repeatedly. The same edge cases get missed. The same architectural directions get proposed, piloted, and quietly abandoned without any record of why. Each new group treats the domain as a fresh problem rather than building on what was learned before.

Common causes

Thin-Spread Teams

When engineers are rotated through a domain based on capacity rather than staying long enough to build expertise, institutional memory does not accumulate. The decisions, experiments, and hard lessons from previous rotations leave with those developers. The next group inherits the code but not the understanding of why it is structured the way it is, what was tried before, or what the failure modes are. They are likely to repeat the same exploration, reach the same dead ends, and make the same mistakes.

Read more: Thin-Spread Teams

Knowledge Silos

When knowledge about a domain lives only in specific individuals, it evaporates when they leave. Architectural decision records, runbooks, and documented post-mortem outcomes are the externalized forms of that knowledge. Without them, every departure is a partial reset. The remaining team cannot distinguish between “we haven’t tried that” and “we tried that and here is what happened.”

Read more: Knowledge Silos

How to narrow it down

  1. Do post-mortems show the same root causes in the same areas of the system? If recurring incidents map to the same modules and the fixes do not persist, the team is not accumulating learning. Start with Thin-Spread Teams.
  2. Are architectural proposals evaluated without knowledge of what was tried before? If the team cannot answer “was this approach considered previously, and what happened,” decisions are being made without institutional memory. Start with Knowledge Silos.

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