Scenario: In your ETL testing project, you encounter a situation where the data extracted from the source systems does not match the expected data in the target system. What steps should you take to identify the root cause of this discrepancy?

Comparing data at each ETL stage involves comparing the data extracted from source systems with the data at various stages of transformation and loading in the ETL process. This helps identify discrepancies and pinpoint where data integrity issues may have occurred. By systematically analyzing the data flow and transformations at each stage, testers can identify the root cause of the discrepancy and take appropriate corrective actions to ensure data consistency between source and target systems.