I had to memorize multiplication. We weren't taught any other way. 3x3 = 9 because it just is that way, memorize it. I had stacks of flash cards. My mom struggled so hard for weeks to teach me my multiplication tables at home. In the end, I (somehow) passed the multiplication quiz or whatever and did my best to do as little multiplication as I could for the rest of my life. As a result, I still have never learned all the multiplication tables, and have a deep dislike of math or numbers in general.

I bet my education would have been a lot different if I could have learned how to multiply effectively from a young age.