3 weeks of practice boards vs my first real case, the difference was wild

Last January I finally got brave enough to rebind a water damaged copy of Moby Dick I bought for $2 at a library sale in Tucson. My first 3 practice boards looked like a toddler cut them with safety scissors, gaps everywhere and the corners were mushy. I started cutting my boards 2mm bigger than the text block and sanding them flush after gluing, and the change showed up fast, maybe by board number 8. By week 3 my hinges actually opened flat instead of cracking when I turned a page. The other thing was grain direction, I had been ignoring it and a bookbinder at a swap meet in Mesa told me to always run the grain vertical on the spine. Once I did that the boards stopped warping after the paste dried. Anyone else remember the exact project where it finally clicked, and what was the one trick that did it for you?