You cut up an elephant when you know it is an elephant. With complex undertakings, cutting it up before you start is not the solution. It is the first mistake.
„Slice the elephant“ is the standard advice for large undertakings. It works as long as the problem is only complicated. The complicated you solve with expertise, structure and clean analysis. The complex you solve differently: with an iterative approach, feedback loops and adaptation. In a transformation the core is rarely just the technical implementation. It is the social and organizational interplay, and that is mostly complex, not merely complicated.
Why the plan comes later
When I take over a program, the first step is gathering information, while the expectation is often already results. I question externals and interview internals: what is the situation, what has happened so far, what is really needed, what was promised, where did it fail. History, present, planning. That takes time, and until this phase is done, it only goes roughly. You rarely get away entirely without an estimate, but then it is experience values with a broad corridor, not false precision.
In a Europe-wide compliance program we treated both sides separately. The complicated side we got a grip on with a pre-project: internal assessment of what we need and what we can do, plus external advice on exactly what the requirement looks like, and on that basis the planning. The complex side could only be untangled in practice. How strictly do the national authorities really act, what do our own first experiences show, should we scale back or build further. That stands in no plan, you learn it by doing.
When a detailed plan does harm
A detailed plan becomes actively harmful when it promises false precision where an honest answer would have been needed. It gives the decision-maker a certainty that cannot exist yet at that point. The exception is hundred-times-rehearsed templates, where you really do know. For a four-week project, planning to the hour is fine too. For a multi-year initiative, the last year should hold only a rough milestone. Whoever delivers hourly plans there is, out of insecurity, selling a precision that the first real project experience does not survive.
Ask with every detailed plan: does someone here really know, or is the precision merely selling safety? A roadmap for a multi-year undertaking is a compass. It is not a GPS.