Apache Druid manages data retention using load rules to transition segments between historical tiers and ultimately purge them from the cluster. A common misconception about these rules is that their retention periods are consecutive, while in reality, they overlap. This misunderstanding can lead to premature data removal, as illustrated by a scenario where only 5 days of data are retained instead of the expected 7. The article explains how to correct such mistakes and recover segments before their permanent deletion, highlighting that segments marked as unused are still stored in deep storage and can be restored unless deleted by the coordinator kill task. The default settings in Druid generally prevent automatic segment deletion until they are 90 days old, allowing recovery through the "Mark as Used all segments" function. This recovery process, which re-applies the load rules, ensures that previously affected data is reloaded and accessible until it naturally ages out. Understanding and adjusting these load/drop rules are crucial, but fortunately, errors are correctable if the segment data and metadata have not been permanently removed.