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. 
• Mitkute explained how she created the app — and why she decided to step away from the business. 

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.