The fact that Gmail doesn't allow you to customize or expand your categories beyond the 4 it gives you frustrate me beyond belief. That, and the fact that there are countless examples of email sources that no matter how many times you move it to the category you want and tell it to "send all emails from x to category from now on," it continues to fail to filter them unless you make your own filter. And then managing the filters is a pain in the ass with a UX that hasn't been updated for 15 years, and also their labeling system is stupid because selecting a parent label only shows you emails with that EXPLICIT label instead of including all children labels.