People are afraid to make thumbnails? There are plenty of tutorials out there, and even apps that simplify the process. Even adding a word or two of big, eye catching text is better than nothing and will make your thumbnail so much more attention-grabbing. And that's super easy. No need to be afraid!
This is important. While there are some apps like Phonto that have good ones, the default fonts on your computer are not very interesting. It only takes a few minutes to find and download a much more interesting font online!Fonts. Fonts can make or break a thumbnail, it's really important that the font you use is very visible and legible. DO NOT USE THE DEFAULT FONTS.