When dealing with busy readers, always put your biggest points up front. When writing an executive summary for a business plan, the concept and how it makes money should be the first two lines, and certainly no later than the first paragraph. As they say in journalism, "Don't bury the lede!" It's important because busy readers will only listen to your justification IF they find the assertion itself interesting. They won't wait around to see if your idea was worth the wait.
The idea of pitching your idea first, and then providing the supporting information is called reader's logic. Conversely, writing through a thought process, and leading the reader to a conclusion, is called writer's logic. Reader's logic is most often found in good business writing and journalism, while writer's logic is prevalent in engineering and the sciences. You can see that the areas where reader's logic is more widely used are those that cover a wider array of topics - as such it's important to let the reader know what the main idea is up front - and let them decide whether to invest the time to read further.
However, this isn't a magic bullet, and it does come at a cost. Reader's logic doesn't allow you to draw the reader in as much, or engage them as deeply. For that reason, most of my posts on this blog use writer's logic. This style also makes it much harder to present ideas that the reader will view skeptically - since the ideas are up front, you have no time to "ease" the reader over to your point of view.
So, whether your reader is a busy VC that gets dozens of business plans every week, or a harried TA trying to grade 50 papers during finals week, make sure to get your most important points across using reader's logic.
This post is a rewrite of an older one, designed to illustrate the differences between these two styles of writing.
Update: As usual, Seth Godin says it better than I ever could.