Psychiatrists use an old trick to get people to trust them with their secrets - and it works just as well in business

There's a common misconception that trust is something that builds gradually - that the only person you could possibly reveal personal information to is a close friend or family member you've known for years.

And yet one of the best nuggets in "Friend and Foe," a 2015 book by the psychologists Maurice Schweitzer and Adam Galinsky, debunks that idea, instead suggesting that there's a somewhat scientific formula to gaining people's trust quickly.

It's less creepy than it might sound. The key is simply to strike a balance between warmth and competence - so that you seem credible but also human.

This idea is based on a 1966 study by Eliot Aronson, which found that "pratfalls," or minor screw-ups, can increase people's appeal. For the study, male college students listened to tape recordings of people supposedly trying out for the college Quiz Bowl team; some candidates seemed highly impressive, while others seemed less so.

In some cases, the candidate spilled a cup of coffee all over himself; in some cases, he didn't. Results showed that students liked the impressive candidates better than the less impressive candidates - but they liked the impressive candidates even more when they spilled their coffee.

To illustrate how this theory works in the real world, the authors use the example of psychiatrists, whose job is to get people to open up about their deepest anxieties and insecurities.

One of their former executive-education students, a psychiatrist named Tom, would employ one of three tactics when he first met a new patient: he'd drop a pencil, tell a bad joke, or spill his coffee.

Presumably, Tom's patients had already been impressed by the diplomas on his wall, which signaled his competence and credibility. Now Tom's goal was to demonstrate some vulnerability and show that he was indeed a fallible human being. That combination of competence and warmth would make him seem more trustworthy.

This technique works just as well in the business realm.

The authors cite an example of an American engineer who was working at a company in Japan. The engineer was annoyed that he was continually listed as a visitor in the minutes of the meetings. But after he joined his Japanese coworkers for a night of karaoke, they started listing him like the rest of the staff.

The authors' takeaway is that highly competent people can make themselves seem more approachable, and more trustworthy, by being a little clumsy or silly. It makes them seem vulnerable and warm.

"The effectiveness of this strategy debunks the common assumption that trust is something that can only be built slowly over time," the authors write. "By making yourself vulnerable, it is possible to build trust in less time than it takes to mop up a spilled latte."

The two caveats here are that you must demonstrate credibility before you exhibit vulnerability - otherwise the formula won't work.

Moreover, you can't demonstrate vulnerability in a way that undermines your competence. For example, a surgeon obviously couldn't drop his tools and feign clumsiness.

Bottom line: If you want people to trust you, first impress them with your knowledge and capability, and then show them you're a human being just like they are. Again, it's nothing sneaky - it's about giving people a full picture of your abilities and personality, and ultimately letting them make the decision about whether to open up to you.