A validation rule can enforce data quality by preventing users from saving records that do not meet certain criteria. In this case, the validation rule can check if both the Sales Engineer and the Account Executive lookup fields are blank, and display an error message if so. This way, the director of sales can ensure that every opportunity has either a sales engineer or an account executive assigned to the deal. References:
https://help.salesforce.com/s/articleView?id=sf.validation_rules_overview.htm&type=5