The thumbnail is what gets someone to click, but the content is what makes them stay. If your thumbnail is dull or confusing, most people will scroll past without giving the video a chance, no matter how good it is. But if your thumbnail is eye-catching and your content disappoints, people will leave quickly and that hurts your performance over time. Both matter, just at different stages. Do you think creators spend enough time designing thumbnails compared to the time they put into the actual video?