Forrester argues that AI can map how legacy applications behave but not why they were built that way. Analyst Biswajeet Mahapatra says AI can read source code, configuration, incidents and change histories far faster than people. Discovery tools then link applications, data, services and business rules into a connected map. That exposes hidden dependencies, duplicate logic and integration risk before a rewrite starts. But a rule in code may be a legal obligation, an obsolete policy, a workaround or an old bug. Only the people who run the system can say which rules belong in the new version. Forrester says most modernisation programmes fund the automated half and skip the human half. It warns that access to business experts becomes the new bottleneck on delivery. Without a target architecture, AI reproduces the old design in new code. Forrester advises setting domain models, integration patterns and security controls first, then letting AI build within them.