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My situation looked dire. I was in Nice, France. The last train had left without me. I didn’t know the town, the language, or anyone for miles. I would have to either convince a stranger to put me up for the night or sleep on the streets. Okay, fine, I could have gotten a hotel, but that wasn’t the point: I intentionally stranded myself to see how good I had become at creating fast relationships. More on that later.

I’m a behavioral scientist studying, among other things, networking and adventure. While researching my book, The 2 a.m. Principle: Discover the Science of Adventure, I needed to understand how to build meaningful relationships quickly. In that time, I battled Kiefer Sutherland in drunken Jenga and crashed his Thanksgiving, was crushed by a bull in Pamplona, and within ten seconds of meeting, built enough trust with a duty-free cashier in the Stockholm airport, that she left her job to travel with me and my entire family (all 13 of us) for an entire week.

Here are some of the most important science-backed lessons you should know:

Litmus Tests

Don’t invest too much time engaging with the wrong people. When approaching someone, begin with a litmus test. Similar to those color-changing strips from science class, these social tests quickly tell you about a person’s personality. Organizational psychologist and famed Wharton professor Adam Grant suggests asking people, “How much does the average employee steal from a crash register in a year?” The higher the number the more likely they are to be dishonest. The reason, Grant explains, is that people assume others are like them, and will act as they would. This is of course not definitive but suggestive. If you want to find out if a person is adventurous, ask them: “What’s the wildest thing that you have done on a dare?” If you wave at someone from across the room and they wave back, they’re friendly, you can approach. One way to tell if someone’s self-centered is to ask them to draw an E on their forehead. According to Harvard Business School professor Francesca Gino, author of Sidetracked, if the E faces you, they focus on others, if it faces them, they’re probably self-centered.

The Ben Franklin Effect

Get people to invest effort in you. Ben Franklin won over a rival by asking to borrow a rare book. Research has shown that you can bond quickly with strangers by asking small and then progressively larger favors. Each time they invest effort into the relationship they will like you more. Start by asking them for the time or to take a photo and build the requests and relationship from there. This doesn’t mean trying to con people or becoming overly needy, mind you. Relationships are a give and take, so reciprocity is critical. Begin by asking an acquaintance for coffee to learn about their industry, and then ask them for a few introductions, but find a way to provide them value in return.

Find your shared background

We are wired to be attracted to the familiar. To give you one example, a team and I conducted research that showed we are 11.6 percent more likely to date people with our own initials. We quickly connect with people of the same school, organization, religion, etc. If you have differing backgrounds, bond over a shared activity. Whether that’s sweating together at a gym or working together at an office, by having a shared goal you create faster relationships.

Use the Misattribution of Arousal

Take the pressure off yourself and leverage fun shared experiences. Research from the University of British Columbia found that when in exciting situations, people attribute their feelings to the people they’re with, not just the experience. You may seem funnier by taking a date to a comedy club or more attractive by participating in daring activities. Technically, it’s what’s known as misattribution of arousal, which isn’t necessarily sexual arousal, per se, but physical arousal of the heart rate, adrenal gland, and hormones.

Finish strong

If a perfect date ends on a negative note, you’ll remember it negatively. The reason is explained by what researchers call “The Peak End Rule.” We don’t remember the duration of pleasure or pain. We remember peaks of experiences and how they end. If you drag out your experiences, the momentum and enjoyment will fall. They will end on a lower note, and people will remember you less fondly.

Thanks to these and other techniques, I spent that night in Nice in a three-story château near the border of Monaco. I had my own room and was hosted by British title holders and extended royal family. After failing to connect with countless people, I went to a bar and toasted four strangers (a litmus test). This led us all to have another round, their treat (Ben Franklin effect). As the drinks poured, so did the excitement of the night (Misattribution) and they invited me to crash in a guest room. There’s nothing like making fast friends on the road.