IAM decisions combine applicable policies and constraints. Explicit denial can override otherwise allowed actions, so one allow statement is not the whole decision.
Before you start
You should understand regions, identity permissions and the responsibilities of the AWS service being discussed. Sketch request flow and failure boundaries before choosing configuration. Work through these scenarios as designs; provisioning real resources can introduce charges and requires an account-specific permissions and capacity plan.
The practical goal is to reason through this situation: A role may allow an action while an organizational control denies it. Read the walkthrough first, then try the interview exercise before opening its answer. The important part is explaining the decision and its consequences, rather than remembering a definition alone.
Step-by-step walkthrough
Step 1: Identify the actual principal
Check the assumed role and request context, not merely the intended username.
Step 2: Review applicable constraints
Identity, resource and relevant organizational or boundary policies can affect the decision.
Step 3: Find denial evidence
An applicable explicit deny is not repaired by adding another allow.
Worked scenario
A role may allow an action while an organizational control denies it.
A workload role permits an action, while an organizational policy explicitly denies it. The action remains denied. A missing allow and an explicit deny require different remediation; resource policies, session constraints and service-specific rules also need consideration when explaining the complete request decision.
Common mistake
Adding more allow statements cannot overcome an applicable explicit deny.
Verify the behavior
Inspect the real principal and policy context, then test the narrowly intended permission.
Interview exercise
Diagnose access denied.
Answer and reasoning
Inspect identity, resource and relevant boundary policies, request context and service-specific authorization behavior.
Continue learning
Compare the scenario with the AWS interview questions and test your understanding with the AWS MCQs. For terminology and implementation details, consult the reference material.