Goals are fundamental to measuring the effectiveness of campaigns in Marketing Cloud Personalization. To accurately track performance and attribute conversions, a goal must be defined and active before the campaign it is intended to measure is launched. This ensures that from the moment the campaign goes live, the system can monitor and record all user activities that meet the goal's criteria, providing a complete and accurate dataset for analysis.

A: Defining a goal after a campaign has launched will result in incomplete data, as any conversions that occurred prior to the goal's creation will not be tracked.

B: While new goals are created over time, for a specific campaign, the relevant goals must be defined before launch, not at an arbitrary later point.

C: Reviewing statistics is a post-launch activity. It is too late to define a goal at this stage for measurement, as no data will have been collected for it.

1. Salesforce Help, Marketing Cloud Personalization, Goals. The documentation outlines that goals are used to "measure the success of your campaigns," a process that inherently requires setup before the campaign begins.

2. Salesforce Help, Marketing Cloud Personalization, Plan and Launch a Campaign. The "Before you begin" section of campaign planning documentation implicitly requires that measurement criteria (like goals) are established as part of the planning phase, prior to launch.