Elasticsearch's journey to implement sequence numbers in index operations has been complex yet transformative, significantly improving the system's replication and recovery processes. Initially sparked by a "what if" scenario, the idea was to enable features like a Changes API, incremental reindexing, and cross-datacenter replication, but the implementation turned out to be more challenging than expected. After nearly six years and significant efforts, including a complete rewrite of replication logic and collaboration with distributed systems experts, Elasticsearch introduced primary terms and sequence numbers to resolve operational divergences upon primary shard failures. These enhancements allow Elasticsearch to efficiently manage index operation history, enabling faster recovery by using transaction logs instead of large file copies and setting the stage for cross-datacenter replication. The introduction of configurable translog retention settings in version 6.0 underscores the balance between faster recovery and disk utilization. While the deployment of sequence numbers marks a major step forward, the community continues to explore additional features and improvements inspired by this advancement.