I went through the same thing when I started training in Daito Ryu Aikijutsu, lo these many years ago, wearing a white belt after having been a black belt in Tae Kwon Do for awhile. It's humbling. Then it happened again, with Arnis (blades and sticks, mostly). And lately, Krav Maga/handgun training (we combine the two).
There's always something new to learn, and there's always somebody better!