The 4-word 'hack' confident people use to get others to agree with them—it makes you 'influential,' expert says

Want to win more arguments? Use this simple four-word "hack," says an influence expert: Keep your explanation brief.

The more bullet points you add to your argument, the less persuasive it becomes, says Niro Sivanathan, an organizational behavior professor at London Business School.

"Most people make the forecasting error that in order to win people over, you need to get them lots of data," Sivanthan tells CNBC Make It. "Oftentimes, things fail not in content, but delivery."

It's called the dilution effect: Your strongest claims get watered down the weaker ones. People listening will walk away remembering the average persuasiveness of each point you make, rather than your single most convincing argument, Sivanthan explains.

If you're trying to convince your friend that New York is the best city in the world, for example, you might cite the pizza, Broadway shows, public transit and Times Square. Depending on your audience, some of those points will be more persuasive than the others, and you're better off only using the ones most likely to win your friend over.

"Less is more," says Sivanthan. "If you have just one key argument, be confident and put that on the table, rather than feeling the need to list many others."

The inverse of this strategy also works, according to Sivanthan's research. After watching drug commercials, consumers were more likely to view a drug favorably when the companies listed a moderate side effect right after a severe one, his 2017 study found.

Using the dilution effect to make your arguments more persuasive can be a "very easy fix," Sivanthan says. It can help you land a job, shorten your presentations and make your dinner table debates more cordial.

It does require self-control. Once you've laid out your core argument, you have to be comfortable letting it hover in silence until the other person is ready to respond. Otherwise, you'll find yourself inadvertently jumping in again with additional weaker points.

"People have trouble with silence. When there's an empty space, you feel the need to fill it up with words," says Sivanthan.

It's a common error, even for people who argue for a living, he adds: "You'll see this in political campaigns and debates ..... [They] should have stopped after [point] No. 2, but they'll go to three or four."

Silence is a powerful negotiation tool, and often results in a better outcome for both parties, research shows. Mark Cuban, a billionaire investor on ABC's "Shark Tank," uses the strategy often: After a contestant pitches, he tends to initially stay quiet while the other panelists argue and hash out details.

If he does decide to make an investment offer, it's after he's had time to analyze the strengths and weaknesses of any potential deal, he said during a Fireside conversation in June.

"The more you pay attention and the more aware you are, the better opportunity you have to get what you want," he said. "Silence is ... money in the bank."

That's smart, Sivanthan says.

"A lot of influence is taking the time to think through [arguments]," he says. "Those who are really good at meetings and [connecting] people ... they've given it a lot of thought. It's not by accident."

DON'T MISS: Want to be smarter and more successful with your money, work & life? Sign up for our new newsletter!

Get CNBC's free Warren Buffett Guide to Investing, which distills the billionaire's No. 1 best piece of advice for regular investors, do's and don'ts, and three key investing principles into a clear and simple guidebook.