Whether your topic is simple or complex, you still need to lead with your point. A complex analysis might have many sub-points that you prove-up in subsequent paragraphs, but your ultimate conclusion still needs to come at the beginning, and each supporting paragraph still needs to lead with the sub-point you're proving.

Say you're writing a memo to your boss explaining why you need to double the size of your engineering team. That point has to come first. Now, maybe the reason you need to double the size of your engineering team is that management wants to add new product lines, and customers are demanding more customized solutions. Okay, so each of those points are the leads in their own paragraphs.

Where a lot of people have problems is that their writing is a chronological recounting of their thinking about the issue. So it starts somewhere in the middle where they encountered some part of the overall issue, then backs up to where they recognize the larger issue, and then buries the solution at the end.

The structure you were taught in high-school: topic sentence, supporting sentences, conclusion, is simple and appropriate for business communications. There are some writers who can clearly convey complicated thoughts using a more narrative structure, but you'll rarely go astray sticking to that basic style.

Yes, lead with the point. I can't tell you how many emails I get that are written like a movie or TV script. (Better not spoil it for the reader; we'll just barely foreshadow the point and there's more coming up after this commercial break...)

Even worse is wading through one of these tomes, only to read two or three possible courses of action with none recommended above the other(s).

tl;dr

Complex or simple, lead with point. Because reasons.

Intro, support, conclusion -- do it.

In my experience, the higher you go in an org, the more terse and direct the written communications is. At the IC & supervisor levels, folks tend to write books in email, often because they feel obligated to provide a complete justification for their decisions (or ideas). As you go up the decision-making ladder, the need to explain oneself shrinks (at least, this is the perception. Strong leaders will do it regardless.)

The other issue is that for folks low on the food chain, they often don't feel comfortable requesting face-to-face meetings with execs, and "manage up" by providing absolutely as much detail as possible to their direct management in hopes he/she will do it on their behalf. Again, an organizational deficiency, but a common one, and one that's easy to understand.

Concision & clarity of communication are critical tools in any employee's toolbox. As an aside, this is one reason it's pretty easy to find articles and blog posts endorsing the success many liberal arts majors have in the tech world.

This concept is will known in the military as BLUF - bottom line up front. Not an abstract or introduction, putting the key recommendation or outcome at the beginning. It falls in and out of fashion but as with newspapers it helps you work out what you want to read further.

Known on the internet as TL;DR

Tl;dr is an antipattern, and it's easy to see why.

Lead with a strong point. Pique youre reader's interest. Then, and only then, will they lap up your wall of text. Tl;dr is a gag, a joke, mockery of bad writing style. If you find yourself using it in a serious way, as a crutch, stop, rewrite, don't go down that path.

TL;DR doesn't always appear at the beginning which is what cmdkeen was talking about.

It's even possible to write simply about complex topics. Nobel Prize announcements are especially good at this, see e.g. http://www.nobelprize.org/nobel_prizes/physics/laureates/201.... Obviously nobody's going to walk away from a summary with a full understanding of a deep subject, but some of the key ideas have been conveyed.

If it's an academic paper, by all means, be complex.

But if its an article meant for the general public, it's your job as a writer to make it more palatable.