When a customer says “I could not pay”, seeing only an error message is not enough. You need to understand which service the request passed through, how long it took, and where it was cut off.
Three different signals
Logs record a specific event, metrics measure the system over time, and traces show the path a single request follows across services. Read together they turn generic sentences like “the server is slow” into a real diagnosis.
What does a good log look like?
It should hold the event time, service name, request ID, result, duration and a safe user context. Logging passwords, tokens, card details or unnecessary personal data is not observability — it creates a new data risk.
Business metrics first
Alongside technical metrics, track business outcomes like successful payment rate, order completion, form abandonment or support response time. Even if the system works well, the customer flow can still deteriorate.