It's crucial then to use your best communication skills. That main message should be a firm assertion of what you want to accomplish. Leading up to that message with background information only invites objections and side discussions and by the time you get to the main point, the other person won't even hear you. The more aggressive or evasive the other person, the more important this principle becomes. Present only your strongest arguments.
Many people think the more arguments, the better.
The opposite is true. You need few arguments but good ones. Anything weak is just an opening for objections and sidetracking. So keep minor arguments as backup. Nothing impresses people more than being really listened to.