Vinted was my 2 a.m. house party idea. I didn't think people wanted to buy secondhand clothes online, but I was wrong.

• Milda Mitkute is the cofounder of one of the secondhand shopping app Vinted.
• It operates in 16 countries and was Lithuania's first "unicorn" company valued at $1 billion-plus.

This as-told-to essay is based on a conversation with Milda Mitkute, the cofounder of second-hand shopping app Vinted. The following has been edited for length and clarity.

Vinted created me as a person, and as a professional.

I was in my early twenties and had just moved to Vilnius, the capital of Lithuania, to complete a master's degree.

The apartment I was moving into came with a much smaller closet than I had at my mum's house. I couldn't take all my clothes and as I was going through them, I realized I had more than 100 items that still had labels on or I'd only worn once.

I had this selfish goal of getting rid of my stuff and was also curious to browse other girls' closets.

Sometimes selfish goals help to create big things.

A completely organic process

By chance, a few days later I was at a house party and I met Justas Janauskas, who was a developer. It was 2 a.m. but we started talking about this idea.

"Okay, let's meet in a few days and think about the name, about action planning, and so on," we said.

Neither of us had any business experience, but we worked out a plan to launch the site. "Give me two weeks to design a site," Justus said.

He came back to me in 10 days and said he'd done it.

I took pictures of my clothes and uploaded them on the weekend. We emailed friends asking them to add items so that we could make the catalog bigger for the launch.

We didn't have money for marketing, but some of my friends had studied journalism and I guess it must have reached media contacts because within a few hours of that email going out radio stations and newspapers started to call us.

Within a few weeks of that party the first version had launched.

European expansion

For the first three years, we were both still working in normal jobs — I was completing my master's in culture management and working at a PR agency, and Justus was an IT engineer.

The biggest cost we had was paying for the servers. It was 10 euros (about $10.80) a month and we'd track it on an Excel sheet. But when you have 30,000 people on your site you need more servers and those invoices started going up to 200 euros.

I was only earning 500 euros a month, so that was a fifth of my salary.

We started adding advertising on the site to cover the costs and then created an entity. That's how we became a self-sustainable business.

There was no macro analysis, no budgets, nothing. But we were booming. By 2011, we were in the Czech Republic and Germany, and growing 60% or 70% a month.

Top companies in Lithuania started offering to buy us, but we rejected all of them — this platform was our passion and we didn't want to lose that opportunity.

Then, our first business "angel," Mantas Mikuckas, joined Vinted. He was the one to say, "let's try and spread this movement all around the world."

We expanded the team, focused on design usability, and developed the app, which was a game changer.

In 2013, Accel Partners, the guys who invested in Facebook and Spotify, said they'd fly out to meet us immediately. They put in $5 million.

It felt like we were students who had just been handed all that money, but we used that moment to really identify what we were as a company — secondhand clothing first.

We are more similar than we are different

We had thought that buying secondhand was a post-Soviet Union concept — if you didn't have money, you go and buy somewhere else — and didn't expect that other markets might be interested as well.

But when we asked girls in Germany, France, and the US why they used Vinted, it was all about selling to earn some extra cash, authenticity, finding unique clothes, and consuming more sustainably.

For us, it was an eye-opener. Our business could be successful across borders with this internet-native generation.

Looking back, it would have helped to do more research about the competition. But in some cases when you don't know what challenge you're up against, you just don't have to fear it.

A life divided into projects

When you're young you think that the more you work, the more you're going to create. In some cases, that's true but on the other hand, you just get exhausted.

I had no social life. I would go into the office every morning at 6 a.m. and not leave until 10 p.m.

Now I would do lots of things differently. I'm 38 and I have much more experience. I know how to create balance. It's not only about business. Everyone has other sides as well and other parts of their character to explore.

So when I turned 30, I decided that it was time to pause the Vinted project and start a family project.

My husband and I both quit our professional lives to be there full-time for our children. I won't lie, we did have a babysitter to help, but we wanted our children to remember that we weren't exhausted all the time.

After seven years, I have four kids. I've also used the time for personal development and completed two more master's degrees. It's been so important to just hear the thoughts in my head.

But I'm closing the family project and developing a small edtech startup.

I still shop on Vinted and my kids use it too. We have a rule: if you want to earn pocket money, resell stuff.

Mitkute stepped down as CEO in 2017 and is no longer on the board but remains a shareholder. Vinted was last valued at about $3.8 billion.