To determine success metrics for Facebook Live, we would need to consider the objectives and goals of the feature. One potential objective could be to increase engagement and time spent on the platform. In this case, we could measure metrics such as the number of unique viewers, the number of comments and reactions, and the average time spent watching a live video. Another objective could be to drive revenue through advertising. In this case, we could measure metrics such as the number of ad impressions during a live video, the click-through rate on those ads, and the resulting revenue generated. It's important to keep in mind that success metrics should be tied to the overall goals of the company and the product, and should be regularly reviewed and adjusted based on the performance of the feature. Additionally, it's important to consider the user experience when measuring success metrics, as metrics that negatively impact the user experience may not ultimately lead to long-term success.