The problem you generally face as you sit down to write is that you know roughly what you want to write about, but not specifically what you want to say or how you want to say it. This sense of uncertainty persists despite knowing that the ideas you eventually put down, whatever they be, must end up forming a pyramid.

Nevertheless, there is a good deal you do know about your end product that you can build on. To begin with, you know that you will have a sentence at the top of the pyramid that will have a subject and a predicate. You also know that the subject of that sentence will be the subject of your document.

In addition, you know that the sentence will serve as the answer to a question that already exists in the reader's mind. And that question will have arisen because of a situation (with which the reader is familiar) within which a complication developed (with which he is also familiar) that raised the question that caused you to need to write in the first place. You may even know roughly some of the points you want to make.

That is quite a bit to know. You can use this knowledge in building your pyramid either by starting at the top and working down, or by starting at the bottom and working up. The first way is generally easier than the second, and so should be tried first.