The document discusses 4 secrets for maintaining fitness in an SAP BW system. It shows that most data in a typical BW system is not report data but rather temporary, master, or cube data. It identifies 4 categories of BW fitness to focus on: system robustness, data quality, query performance, and information lifecycle management. It provides tips in each category, such as regularly checking for unused IDs, building indexes and aggregates to improve query performance, and using nearline storage to archive cold data and reduce data volumes over time.