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The cost YAGNI was never about

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June 28, 2026

4 min read

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Summary

YAGNI (You Aren't Gonna Need It) is a principle that emphasizes not implementing features until they are necessary, countering arguments for premature complexity. The principle is often misunderstood as merely about saving effort, but its true focus is on avoiding unnecessary complexity in software development.

Key Takeaways

YAGNI (You Aren't Gonna Need It) is not about saving effort but about avoiding speculative structure that can lead to unnecessary costs.
Building structure before a feature arrives incurs two costs: optionality loss and net present value (NPV) loss, regardless of whether the initial prediction is correct.
Waiting to build until the need is clear preserves the option to create the right structure and avoids premature costs.
The cost of typing code is not factored into the two main costs associated with YAGNI, highlighting that the focus should be on timing and necessity rather than effort.

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Community Sentiment

Mixed

Positives

AI has significantly reduced the costs associated with restructuring code, enabling developers to implement changes more efficiently and safely.
The ability to quickly and safely change significant parts of the code is now a top priority, highlighting AI's role in enhancing productivity and flexibility in software development.
Building speculative structures can help expose failure modes earlier, making it easier to identify necessary features and requirements in an AI-enhanced development environment.

Concerns

Relying too heavily on AI may lead to a lack of critical thinking, which can result in being outcompeted by those who leverage AI more effectively.
There is a risk that building speculative structures without proper consideration can lead to 'slop', undermining the quality of the codebase.