In Joe Elliott's guide on diagnosing dropped spans in Jaeger distributed tracing, the focus is on understanding and addressing the loss of critical spans within the Jaeger span ingestion pipeline. The guide highlights the importance of refreshing the Jaeger UI before diving into infrastructure diagnostics, as traces might not be fully ingested initially. It details the Jaeger setup from the in-process client to the Jaeger Agent, Collector, and Ingester, emphasizing the use of metrics such as jaeger_tracer_reporter_spans_total and jaeger_agent_client_stats_spans_dropped_total to identify where spans are being lost. The guide suggests increasing queue sizes, reducing latency, and optimizing the placement of agents and collectors to mitigate span loss. It also discusses the potential issues with using UDP for communication and recommends reviewing network metrics if packet loss is suspected. The guide concludes by underscoring the role of effective queue management in reducing dropped spans and encourages exploring additional metrics provided by Jaeger for a more comprehensive understanding of the system's behavior.