When a data lake spreads across an organization, two problems immediately surface. First is permissions. When all data is collected into S3, the sales team must not see PII columns, the Korean branch must see only Korean region rows, and if you start manually managing permissions for every new table, governance collapses. Second is real-time ingestion. When you must handle "data streaming in by the second" instead of batch loading once daily, which streaming platform and how you operate it determines the architecture.