Knives and scissors can be hard to get sharpened. Curved knives, for example, cannot be sharpened on a whetstone due to the shape. Serrated knives will ruin the stone leaving marks on a perfectly flat surface. To sharpen a serrated or curved knife, I have a good set of electric grinders.
Thankfully curved knives don't live in every kitchen.
Speaking of flat stones (not the flat Earth), in my experience, flattering tools never found their use in my inventory. When I work with a new whetstone, I work from the center of the stone out, giving it the U shape. This shape helps me to be more precise with the angles that I give to each knife. Knives can be separated into groups by their cutting-edge angle. I talk about it more in the Knife Bevels
Essentially, you need to work with your stone, each strike gives a new shape to it, as well as to the knife. Once you learn how to focus on areas on the stone's surface, you will understand how to shape your stone the way you want and that works best for you.