Several years ago, on a beautiful Valentine’s Day evening in San Francisco, a friend of mine and I decided to visit the California Academy of Sciences. The museum was love-themed for the occasion, with lectures about dating and exhibits of ancient dildos, contraptions that resembled medieval torture devices.

After perusing the historic sex toys with growing horror, we wandered into a lecture where a woman was sharing the pros and cons of various online dating sites. Her talk led my friend to suggest I create a profile on OkCupid.

I had just moved to the Bay Area and wanted to meet people, but I wasn’t ready to date. So in the “You should message me if — ” section, I wrote a paragraph about why someone should not message me. At the top of my list: “Don’t message me if you’re interested in dating.”

A couple of days later, I received a message from someone who claimed that we had a lot in common, but he insisted I answer more than just 25 questions so he could “more reliably assess” our compatibility. Curiosity drove me to his profile, where I noticed that he had answered nearly 500 questions.

Turns out he, too, had created an elaborate “do not message me if” list that included everything I would have written if I had spent more time on my profile.

We agreed to meet that weekend at a coffee shop. He was thin, with blue eyes and brown hair, and he had the quintessential San Francisco geek look. To complete the stereotype, he was a founder of a tech start-up, the San Francisco equivalent of meeting a writer in Hollywood. The only thing that stood out about him, other than his Slovene accent, was his glasses. Rather than resting on his ears as normal glasses do, they clung to the sides of his head like a huge spider. (It didn’t look quite as odd as it sounds.)

We grabbed lattes, settled in on the patio and dived straight into deep conversation about politics and our pasts. There was no chitchat about the weather or hobbies. Coffee turned into dinner, and we spent the entire evening discussing everything from religion to robotics, unearthing one surprising commonality after another.

We’re both tech geeks, but our overlap went way beyond that, with us sharing identical first jobs, worldviews, everything. Even our mothers seemed like the same person. We stumbled upon the odd fact that each had urged us (inappropriately) to frame and display our I.T. exam certificates from Microsoft because Bill Gates had signed them. Neither knew much of anything about our work, but both had heard of Mr. Gates.

By 10 p.m., we decided to call it a night. He had taken the local rail to meet me, so I offered him a ride home. Our experiences and personalities were so strikingly similar I couldn’t help but wonder if this encounter was an elaborate practical joke orchestrated by my friends. As he told me how to drive to his place, my suspicion only grew, because he was directing me to my own apartment. It turned out he lived right across the street from my building, a fact neither of us had known when we met a few hours earlier.

To uncover our differences, I spent the week answering every question he had answered on OkCupid, but I only found more similarities. I had to supply my answers before I could see his, but one after another, our answers were identical. We met the next weekend for dinner, where I spent five hours looking for reasons to vehemently disagree with him on something, anything.

After three months, the only disagreement we had was over apples; I liked them, and he didn’t. But here’s the thing: Our ridiculous lack of differences worried me. My idea of a successful relationship had been that of a Venn diagram with a healthy intersection, not two mostly overlapping circles, and that the best match was one in which you complemented, not replicated, each other. Perhaps I was missing something.

“Dinners and weekend activities are great,” I blurted out one day. “But we need to find a more efficient way to uncover our real differences.”

“I think we both have the same goal,” he said. “What do you propose?”

In software development, you sometimes intentionally push the boundaries to see if a system breaks. It’s called stress testing, similar in concept to the treadmill test a doctor performs to measure a patient’s heart condition.

“Why don’t we stress-test our relationship?” I asked.

He was game, so we spent the next 30 minutes discussing details. In essence, we wanted to try to create the environment of a decades-long marriage to see how well our relationship might hold up. He would move in with me for four weeks, during which time we would go about our lives without any facade: avoiding romance and doing nothing to try to impress the other person, while being vocal about disagreements and upfront about our inadequacies.

In addition, we created exit criteria. If during or after the stress test either of us felt the relationship wouldn’t work, we would part amicably without drama or guilt.

With our terms agreed upon, he moved in the next day (it was quite convenient that he was already my neighbor), and our test began.

I don’t usually wear makeup, and he had never seen me use anything other than lip balm, so there wasn’t much to test there. But what about hairy legs? That I could do. If I lived with someone for five years (or even five months), there would be plenty of times when he would have to deal with my not-so-smooth legs.

Within a couple of weeks, I had achieved what my ex used to call, “Wookie legs.” To amplify the effect, I wore shorts. Then I wandered around the living room where he was crouched at the desk working on his laptop.

“How is it going?” I asked casually.

“I’m almost done,” he said without looking up.

“Oh no, my T-shirt is stained!” I said, pointing to an oil stain from a previous cooking experiment.

“That’s barely noticeable,” he said.

That stain wasn’t the only thing he was barely noticing. “Does this bother you?” I asked, pointing to my legs.

“Does what bother me?”

“Hair on my legs.”

“Why should that bother anyone?” He went back to fixing his code. Just like that, he made the obligatory nuisance of shaving in winter a thing of the past.

To test his propensity for jealousy and insecurity, I left him alone most evenings to go out for dinner and movies with my friends. But he was fine with the solitude, and all it did was make me exhausted from so much socializing. Once I hit my 30s, my appetite for “hanging out” had declined significantly. All I wanted was to watch a documentary in my pajamas and go to bed early.

For his part, he slept late every day, left coffee mugs on the night stand and set the thermostat to a balmy 75 degrees, all things his ex would have thrown a fit about. Yet I couldn’t even pretend to get upset since they were things I normally do, too.

He also let his goofy personality re-emerge, dropping the guard he had put up after mangling our first intimate encounter before our stress test began.

The first time he came to my apartment, I was busy researching something on my desktop. He stood there looking restless.

“Is everything O.K.?” I asked.

“Would you mind if I did something?” he asked, looking me straight in the eye.

I was nervous, thinking he wanted to kiss me. “Maybe,” I said.

The tension was mounting. Then he walked up and continued past me to my desk. The next thing I knew, he was changing the power settings on my desktop and laptop so they would use less energy when idle.

I burst out laughing, though I didn’t immediately explain why. When he eventually learned that I had expected him to kiss me, he was so embarrassed it made him even more cautious about what he said and did around me.

During our stress test, however, I knew he was back to his old self when instead of saying, “I missed you!” in some generic way, he would hug me and say things like, “It’s too bad I can’t hold you closer than what is physically possible, which is ironic because atoms are mostly empty space.”

The geek in me truly appreciated this.

After all of our test cases passed and the fourth week ended, we were left with one question: “What now?”

He said he wanted to move in with me permanently. Unable to counter him with any logical reason not to, I agreed. A few weeks later, he proposed, and we married 12 months later.

In the two years since, our Venn diagram of mostly overlapping circles has remained intact.