The most important part of a system is the underlying data.
If you understand the data, you will understand the system.
Oftentimes the data is not understood by any of the stakeholders. Data has inconsistent, unclear, or contradictory definitions. If the time is taken to really understand the data, the system, and the processes become clearer.
Processes are simply functions that move data from one state to another. A system is simply a collection of processes.
When processes are convoluted or overly complicated it is usually an indication that the data is not well understood.