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The Simple Way to Be More Persuasive


Trying to convince a client? Your colleagues? The best way to build an argument is with less, not more

One man talking with a speech bubble including incoherent symbols.

In 2019, Niro Sivanathan, a business school professor, took the stage at TED Talks to give a speech about something most of us could use help with: How to be more convincing. About halfway through, Sivanathan asked his audience to consider TV drug ads. Specifically, the voiceovers at the end of those ads that hurriedly list a drug’s many side effects. Some are major side effects, such as internal bleeding. Others are minor, like itchy feet.

Sivanathan then asked the audience to imagine a sleep drug ad that only listed the major side effects of a heart attack and stroke. “Now, all of a sudden, you’re thinking, ‘I don’t mind staying up all night,’ ” he told the crowd with a smile. “Turns out, going to sleep is important. But so is waking up.”

This idea formed the basis of a study Sivanathan published a couple of years earlier in Nature Human Behaviour, one of the world’s top science journals. It found that people exposed to both the major and minor side effects of a sleep aid in an ad rated the drug’s overall severity to be significantly lower than those only exposed to the major side effects. By listing both major and minor side effects in their ads, pharmaceutical companies weakened people’s judgments of the overall risk of taking a drug and thereby increased the marketability of the drugs.

This finding isn’t limited to selling pharmaceuticals. It’s a well-documented judgment bias called the “dilution effect.” For the past several years, Sivanathan (who earned a Master of Science in Management from Smith School of Business) has taught the dilution effect to students at the London Business School, where he is a professor of organizational behaviour.

He also uses the dilution effect to advise business leaders on how to be more persuasive. The main point he tries to get across when talking to them about the dilution effect: stick to your strongest arguments. Sivanathan clearly knows a thing or two about the art of persuasion. That TED Talk, titled “The counterintuitive way to be more persuasive”, has almost two million views online and was named one of TED’s most popular talks of 2021.

The dilution effect was first used by social psychologists Richard E. Nisbett, Henry Zukier and Ronald E. Lemley in 1981. They found that when research participants were presented with both relevant and non-relevant information about other people, participants made less-extreme judgments about those people than when they only considered relevant information.

In the context of persuasion, weaker arguments tend to dilute stronger arguments. In other words, when we try to convince others by presenting them with all the arguments we have, we actually weaken our case. 

The reason the dilution effect occurs is due to the law of averages, says Sivanathan. When we take in information, we give each piece a weighted score. Strong arguments get a higher score than weak arguments. But we don’t add up all of those scores. We average them. So irrelevant or weak arguments tend to reduce the weight of the overall argument. 

This is why Sivanathan tells business executives and entrepreneurs to focus on their most compelling arguments and ditch the rest. “I see it all the time in M&A transactions or negotiations or pitches to angel investors,” he says. “They pepper their slides with ‘15 ways we’re going to disrupt the fintech industry.’ Or ‘the 10 benefits of this over Uber.’ That’s the wrong, wrong strategy. Stick to your two or three strong arguments and drop all the others.”

Discipline in the pitch

As many of those same business leaders tell Sivanathan, however, it’s not always easy to determine which arguments are the most compelling. How do they figure that out? they ask.

His answer: be disciplined. “All of your arguments may sound good to you and you may be proud of them, but you have to step back, maybe run them by a colleague and really think about which are your strongest. Put those on the table. Leave the others to offline conversations. They can be part of your appendices, but they should never be the central element of your discourse.”

One reason why people don’t narrow their arguments is that they want to cater to everyone in their audience, says Sivanathan. They think that by listing each of their arguments, they’ll reach each of their audience members. But this is short-sighted, he says, because strong arguments tend to land as strong to most, if not all.

There is a slight counterpoint to this, he adds. If you know for a fact that the ultimate decision-maker in the audience will be swayed by one of your weaker arguments, include it. In his experience, however, this is rarely a fact.

In short, Sivanathan says, quality trumps quantity. The delivery of your message is every bit as important as its content. “Stick to your strong arguments,” he says, “because your arguments don’t add up in the minds of the receiver. They average out.”