Modern distributed systems demand observability, the ability to understand internal states from external outputs. Observability is achieved by collecting traces, logs, and metrics to improve performance, reliability, and availability. No single signal is sufficient; it's the combination and correlation of these data that form a narrative for root cause analysis. In monolithic applications, debugging was easier since one service handled a request. In contrast, microservices distribute a request across many services, making it hard to follow a transaction’s path. OTel’s distributed tracing shines here; it propagates context with each request, so you can trace a transaction across service boundaries.