An enterprise consolidates nine systems implementing the same capability into one. What are the risks, and what makes such programmes fail?

Why these programmes fail

1. The second-system effect. The consolidated system is scoped to replace all nine and to fix everything each of them did badly and to unify processes that have diverged for years. Each addition is defensible alone; together they mean nothing can be delivered until everything is delivered.

2. The nine systems are not actually the same. They implement the same capability and encode genuinely different business rules — different regions, different regulatory regimes, different customer segments, and edge cases that look like defects and are undocumented handling of real conditions.

Discovering this during migration, rather than during analysis, is what turns a two-year programme into a five-year one.

3. Perpetual coexistence. Some systems migrate, some do not, and the organisation operates ten systems instead of nine — with a synchronisation layer as a permanent tax. This is the characteristic outcome, and it destroys the business case entirely.

4. The migration is a technical programme with no business sponsor, so it loses priority whenever anything else is urgent.

What reduces the risk

Analyse the variation before committing. Which differences between the nine are accidental — naming, process, technology — and which are genuine domain differences that the consolidated system must support? Standardise the accidental variation and model the genuine variation as explicit configuration or capability flags. Flattening genuine differences produces silent incorrectness, which is worse than the duplication.

Migrate incrementally, one system at a time, each with its own business sponsor, date and benefit. A consolidation that delivers value after the second migration is fundable; one that delivers after the ninth is not.

Make decommissioning the deliverable. A system is not migrated until the old one is switched off. Anything short of that is coexistence with extra steps.

Reserve the right to stop. If after three migrations the variation turns out to be genuine and the consolidated system is becoming a configurable monster, stopping at three is a legitimate and much better outcome than completing all nine badly.

The question worth asking first

Why do nine exist? Sometimes the answer is history and acquisition, and consolidation is straightforward. Sometimes it is that the business units genuinely need different things and consolidation will be resisted because it should be.

The nine systems are evidence about the business, not only about the estate, and reading them that way before committing is the cheapest risk reduction available.