Final answer:
To ensure that a reason is entered when an opportunity is lost and closed, a validation rule is the most efficient option. It allows enforcement of business logic to require a reason for specific record statuses, ensuring data integrity without the complexity of other solutions.
Step-by-step explanation:
In the scenario described, the best way to ensure that a reason is entered if an opportunity is lost and closed is by using a validation rule. Validation rules in a CRM or sales management system allow the enforcement of business logic at the database level, so when a record is updated to a particular status — such as 'lost' or 'closed' — the validation rule can check to see if the accompanying 'reason' field has been filled out. If the reason field is empty, the rule prevents the record from being saved, ensuring data integrity and compliance with the business process requirements.
While other options like a workflow rule or a trigger could also accomplish this, they are more complex to implement for this purpose. Making the field required globally would also not be suitable, as the reason should only be required in specific circumstances. A validation rule is more efficient, as it activates only under certain conditions, and does not rely on additional workflows or custom code that would need to be maintained.