Speakers make or break their speeches – and careers – based on the strength of their stories and their command of the facts in the area of their expertise.

Most often, those speeches are best understood as acts of persuasion. A motivational speech is an act of persuasion, obviously:  the speaker tries to get the audience on its feet and excited about becoming new people in one way or another. Right now, here in the US, we’re already deep into the race to become the next President, with over 20 Democratic candidates and now 3 Republicans all trying to persuade us that they are best suited to be President for the next four years beginning in January 2021.  (If that seems like a long way off to be getting excited already, you’re right.) Less obviously, speeches on other topics are acts of persuasion, too – persuasion about a POV or the rightness of a cause or the need for action in one sphere or another.

The general operating assumption, then, is that stories help in the act of persuasion, by being emotional and memorable, whereas facts persuade us as proof points.

So, how do you weight the two forms of rhetorical persuasion, stories and facts? Is there a way to know when to use one or another? Most speakers just pack as many of both in as they can, time permitting. The more stories, especially, the better.  Too many facts can make a speech overwhelming, or boring, but you can’t possibly overdo the stories, right?

Along comes a new study that finds that there is a situation under which stories actually detract from the persuasiveness of a speech. And that is when the facts are strong.

When the facts are strong, it turns out to be more persuasive to let them stand on their own.  Stories in part disrupt our ability to evaluate facts – they distract us, in effect. So they mask strong facts and make the argument overall less persuasive.

When the facts are weak, on the other hand, it’s better to add the story, distract the listeners, and get them to focus on the emotions and other details. That will mask the weakness of the facts and make them appear stronger than they are. Ms Rebecca Krause, one of the authors of the study, says, “Stories persuade, at least in part, by disrupting the ability to evaluate facts, rather than just biasing a person to think positively.”

It’s not the case, then, that the more stories you have, the better for your argument. If you’ve got a strong case to make via your facts, then let them stand on their own and prove your rightness. It’s only when your facts are weak that you need to bring in stories to bolster your argument.

But there’s a further wrinkle.  Stories still are widely perceived to be more memorable than facts, and there’s lots of good reasons for this to be so. Our memories are stronger or weaker depending on the strength of the emotions we tie them to, and stories are much more likely to have emotions attached than mere facts.  A story of a horrific accident is far more vivid than your last cup of coffee, because of the tragic emotions associated with the accident. Similarly, health scares and other life-and-death moments stick with us far more powerfully than routine meetings or even pronouncements from the top brass in your company.

There may well be times, then, when you’re forced to choose between being memorable or being persuasive – a choice no speaker wants to make. In that case, go with memorability, even if it hurts a little to be thought less persuasive, because that is the deep purpose of virtually every speech ever given.  After all, they won’t be persuaded if they can’t remember it.