YouTube Thumbnail Testing: Clicks vs. Watch Time

The video discusses the importance of thumbnails on YouTube and how success is measured by click-through percentage and average watch time. While A-B testing may show one thumbnail with a higher click-through rate, the true measure of success is the average watch time of viewers who clicked on that thumbnail. This means that even if a thumbnail has a lower click-through rate, if viewers watch a higher percentage of the video, it may actually be more successful. The video emphasizes the significance of choosing thumbnails that not only attract clicks but also engage viewers to watch the content for a longer duration.