Observability
The property of a system that determines how well its internal states can be inferred from knowledge of its external outputs (logs, metrics, and traces).
Impact
In distributed systems (microservices), you cannot "step through" code with a debugger. Observability is the only way to debug complex interactions in production.
Weinto take
Observability is not a tool you buy; it's a property of the code. You must write code that emits useful signals. If you buy Datadog but write opaque code, you just have expensive charts of nothing.