Thixotropy - when a liquid is a solid, and the solid is liquid . . . Everything . . . From the time you pick up the clay, until you lift the glazed ware from the kiln, I've found there are certain things that must be done in certain ways, and without shortcuts. In my quest of making a bowl in a reasonable amount of time, I learned that for every minute you skip kneading the clay, you'll spend fifteen trying to get the pot wall and rim thickness even. Don't dry the pottery completely and it'll blow up when you fire it.
Careful preparation saves time.
It's safe enough relying on 'store-bought' clays and glazes, and most of the successes I'm having now are with them, but to get 'better', or make progress toward becoming a competent potter I must experiment and learn how things work in different ways. I've started making some of my own glazes now and have had some success. I wanted to start with a basic, clear glaze and mixed one according to the recipe, adjusted the specific gravity and dipped a couple of test bowls. It looked good for an instant as the glaze was absorbed into the pores of the bisque, but then the excess around the rim gathered up into rivulets and ran down the sides in sharp, well defined ridges. I read some more, decided it was a 'suspension' problem and modified the glaze batch with some bentonite, a super plastic clay, and it made a little improvement.