Explanation:

- Option 1: Public policy

The doctrine of vicarious liability is fundamentally driven by public policy. This principle holds an employer or principal responsible for the acts of their employees or agents. It aims to ensure victims receive compensation, even if the employer was not directly at fault.

- Option 2: Failure to supervise

This option suggests liability arises from a lack of oversight. While relevant in some contexts, it's not the primary basis for vicarious liability, which doesn't require proof of negligence.

- Option 3: Treated as unauthorized

Generally, vicarious liability doesn't rely on whether the actions were authorized. It focuses on the employee acting within the scope of their employment.

- Option 4: Strict liability

Vicarious liability resembles strict liability but is specifically linked to relationships, not inherently risky activities.