On my right, a girl with bushy hair and a full set of braces was reenacting last night’s episode of Doctor Who. “So Matt Smith leaps out of the TARIDS, grabs Amy and Rory, and time travels to New York. Oh my god. I’m so emotional.”

On my left, a boy with huge glasses was recounting his latest Minecraft session. “So there I am in Infinite Creeper Maze, and I’m like, I wanna kill zombies! and I’m running down the hallway and my friend is like, bro: did you just grab that sword? And I’m like, yeah!”

In walked Mr. Kennedy. He seemed to tower over tiny, 13-year-old me. “Okay, class!” he boomed. “Let’s get started!” After three long hours of class, he concluded with, “Stick around! We’ll be saying some very scintillating things!”

Needless to say, I walked out of the first day of summer writing class feeling extremely anxious. Was this the right class for me? Would I ever fit in with this motley group of sci-fi geeks and video game nerds? What did scintillating mean?

Despite my early anxiety, I realized the kids I immediately dismissed as “geeks” and “nerds” shared a lot in common with me. Eliana and I both loved the Harry Potter series. Jeremy and I were both obsessed with Broadway and musical theater. Ashley and I shared the same sarcastic sense of humor. It’s hard to believe that at one point, I was willing to trust my first impression and distance myself from the people I now consider some of my closest friends. And Mr. Kennedy wasn’t scary at all—he was kind, funny, and shared valuable advice that improved more than just my writing. We’ve all heard the saying “Don’t judge a book by its cover.” So why do we continue to do just that? We hold onto a first impression of someone who could be completely different than what we assume.

Why exactly are we programmed to form split-second conclusions? A New York University study tested the neuroscience of how research volunteers form impressions of each other. While a functional MRI machine scanned for brain activity, each subject was shown a short film of a woman coming home from work. Sometimes the woman was labeled “Janey the Waitress”; other times she was “Janey the Librarian.” The film was otherwise exactly the same. After viewing the film, when the subjects were asked to give their impressions of the woman, they “remembered” details associated with the given profession. If Janey was introduced as the librarian, people remembered her wearing glasses, even though she did not. Our assumptions about how a waitress might behave or the way a librarian might look are so strong that we pay more attention to our own biases than to the evidence in front of us.

When we form these first impressions, we use two parts of the brain: the amygdala and the posterior cingular cortex, or PCC. The amygdala, which receives signals from all five senses, navigates the human social world. It is how we tell friend from foe, sense danger, and develop fear. Without the amygdala, we couldn’t tell the difference between drinking water or drinking arsenic. The PCC is the foundation of your personal memories, your attention, and the emotions associated with memory. This part of your brain is also responsible for predicting outcomes and assessing the value of objects. In other words, when the PCC is active, you remember how you studied for three hours last night for Chemistry to get an A on the test, and how, next time, you’ll do the same thing. When we’re forming first impressions, our amygdala and PCC assign people values based on their outstanding features. Often, these first impressions are lasting impressions. According to the BBC, we can take between 90 seconds and 4 minutes to decide if someone is compatible with us. Your brain takes 55% of this information from body language, 38% from the tone and speed of their voice, and only 7% from what they say. Of course, there’s a reason behind our instinct to form these conclusions in such a short time: to protect ourselves. If you’ve ever changed seats on a bus or crossed the road to avoid someone, you used your ability to form superficial conclusions about someone because you felt a gut instinct that signaled danger. It’s built into our brain by generations of ancestors successfully dodging saber tooth tigers and avoiding the scary people in the next village.

So what should we do: trust our first impressions, or learn more and form a conclusion? Often, when we take the time for the latter, it’s much more rewarding. My freshman English teacher tells a story about the time she went to pick up her son from baseball practice. While she was waiting, she read A Tale of Two Cities, by Charles Dickens. She noticed a teenage boy, loitering in the street, with baggy clothes, long hair, and tattoos all up and down his arms. Wrinkling her nose, she decided it would be best to ignore him. Moments later, he approached her and introduced himself as Daniel. He told her that A Tale of Two Cities was one of his favorite books. Surprised, she explained that she was an English teacher and her freshman class was reading Dickens. She and Daniel had an intelligent conversation about the book—an experience she would recount to her English class every year. Had she stuck with her first impression, she never would have had such a meaningful conversation with Daniel.

Sometimes, blindly trusting your first impressions can be more than inconvenient; it becomes prejudice. For example, the New York police department has applied “stop and frisk” practices to stop New Yorkers for interrogations in the street. From 2002 to 2011, racial profiling was used to stop mostly blacks and Latinos, who were 90 percent of the people stopped. About 88 percent of the people stopped—more than 3.8 million —were innocent. The Federal District Court in New York ruled that “stop and frisk” violated the civil rights of citizens. In this case, skin color—a completely superficial, split-second decision based entirely on first impressions—was the determining factor for those stopped. Even our government, the system we trust to protect our rights, was using first impressions as the basis for their means of law enforcement, with unfair and damaging results.

What can we do to stop these situations? Well, some of it we can’t control. We can’t change our biology and force our amygdala and PCC to stop forming first impressions. But we can make a greater effort to get to know someone before trusting that first assumption. Talk to the geek surrounded by comic books in the library. Sit with the new student sitting by herself in the cafeteria. Start a conversation with the Goth guy who’s in your English class. I’m not saying we should try to completely abandon first impressions—that’s unrealistic, and in some cases, dangerous. But I am in favor of adjusting our mindset to get to know people before relying completely on our superficial judgments.

We can’t solely trust our first impressions of each other as the be-all and end-all of our relationships. Otherwise, we’ll miss out on opportunities to form friendships—whether with sci-fi nerds or unlikely Dickens enthusiasts—that mean so much more than what we assume based on how they dress or how they look. As John Green wrote in Paper Towns, “[It’s ridiculous] that people want to be around someone because they’re pretty. It’s like picking your breakfast cereals based on color instead of taste.” It’s time for all of us to get a second chance at a first impression.