You might have spent a good amount of time on a thumbnail you thought would have done well, only to find out that it flopped. You shouldn’t blame the algorithm just yet; here are some reasons why your seemingly perfect thumbnail didn’t perform.
Maybe you created a thumbnail that would’ve been good in one niche, but you used it in another. Regardless, if you are absolutely sure that your thumbnail has no major flaws (however, see the next section for a different perspective) and that in theory people should be clicking on it, consider that you may be using the wrong thumbnail for the niche of videos you are making.
Your thumbnails might also simply be worse than you imagine. As humans, we are emotionally attached to things we create. It doesn’t matter how good you think your thumbnail is if other people aren’t willing to click. Maybe there is some glaring mistake that you missed in the thumbnail; maybe you just don’t understand what makes a thumbnail “good” (people click on it). To fix this, you either have to be honest with yourself and try to find where you messed up in your thumbnail, or you can ask someone else (preferably a potential viewer, if not a friend) what they like or don’t like in a thumbnail and then improve from there. This is very likely the reason your thumbnails aren’t performing the way you want them to.
Maybe there really is nothing wrong with your thumbnail; however, in that case, you may just be posting at the wrong time. For example, let's say you are making thumbnails targeted towards German people, but you forgot about time zones, and you posted the video while it was night in Germany. Posting at the wrong time will hurt video performance as your target audience just isn’t available to watch your videos. So make sure you're posting at a time where you would get the most potential viewers. To see if this is an issue, simply keep the same style of title and thumbnail while posting at different times; however, this likely isn’t the reason why your thumbnails aren’t performing.
Finally, your title could be damaging your video and thumbnail performance. To determine this, you would have to A/B test the titles with the same thumbnail. Make sure you do this within the first 24 hours of a video being uploaded, as that is the time the video gets pushed the hardest in the algorithm.
There are many potential reasons why your thumbnail didn’t perform well. One might be that you're using the wrong thumbnail for the niche you're in. Another could be that your thumbnail isn’t as good as you think it is. Another reason could be that you posted your thumbnail at the wrong time. Your title could also be damaging thumbnail performance. However, there are many other reasons why your thumbnail didn’t perform: the most important thing you can do is find out why and then fix whatever issues are hurting your thumbnail.