In the dynamic field of API design, the use of sub-resources can introduce significant complexities, as illustrated by experiences from Rebilly and Redocly. Initially, sub-resources like customer subscriptions seemed logical but led to cumbersome processes and inefficiencies, especially when handling tasks such as subscription cancellations and reactivations. This design choice resulted in extensive restructuring efforts to address the inefficiencies. Consequently, the lesson learned was to avoid sub-resources unless absolutely necessary and to consider the full lifecycle of an entity in API design. At Redocly, a rule was implemented to detect sub-resource usage automatically, preventing potential inefficiencies from reaching production. This experience underscores the importance of thoughtful API design and encourages ongoing learning and adaptation in the field.