The Fix

Chapter 13: The Rate Has Changed

The rational response to previous failed modernisations was to leave legacy alone. That calculation is no longer correct: AI has materially reduced the cost of understanding legacy systems, and bounded reconstruction through process-owning units provides a structurally different approach to replacement.

She was thirty-one when the rewrite started and thirty-four when it was quietly abandoned.

The platform was called Horizon, and the brief was to replace the claims management system, a fifteen-year-old monolith, with a modern event-driven architecture that would “future-proof the business.” The senior engineer joined as the second on the rewrite, and she knew the legacy system better than anyone except the contractor who had left the previous autumn. The monolith was genuinely painful, and three incidents in a single quarter traced to the same race condition in the payment reconciliation path, each patched differently because no one could hold the full system in their head long enough to fix it properly.

The first year was productive. She worked with a payments specialist who understood the regulatory constraints better than anyone in compliance, and between them they built a reconciliation service cleaner, faster, and more auditable than anything the monolith had produced.

Then the programme followed the pattern that every practitioner recognises. Engineers rotated off, and their replacements had technical context but not institutional context. Scope expanded as stakeholders discovered late that the new system did not accommodate their process variants, and when the sponsor moved on, the replacement inherited the budget but not the conviction. A consulting firm recommended running both systems in parallel indefinitely, which cost more than either system alone.

Eighteen months later the parallel approach was abandoned, the legacy system remained in production, and Horizon's reconciliation service was quietly decommissioned. The payments specialist left for a smaller company, and the institutional knowledge walked out with them.

The programme budget was € 4.8 million. The opportunity cost of four senior engineers who spent three years building something discarded never appeared in the post-mortem, which attributed the failure to “insufficient stakeholder alignment in the early phases” and recommended a more robust governance framework for future programmes.

She read the post-mortem and recognised the language. It was the same language that had justified the rewrite in the first place. Process ownership, contract enforcement, and budget envelopes require sustained executive mandate; they cannot be implemented unilaterally by engineering. The transition moves authority from the coordination layer to the units that own processes, and that redistribution must be authorised by the people who currently hold the authority.

Every practitioner who has survived a failed rewrite carries the same conclusion: the safe choice is to leave it alone. The hesitation stems from accurate pattern recognition, because the failure modes Horizon displayed are consistent enough to constitute a reliable model, one that has predicted outcomes more accurately than the business cases preceding every failed programme she has witnessed.

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