Y Combinator, the influential start-up accelerator, almost passed on a chance to invest in Dropbox because it had misgivings about bringing on a solo entrepreneur.

After Drew Houston, the creator of Dropbox, scrambled to find a co-founder in time for his in-person interview, the company was admitted into YC in 2007. Four years later, venture capitalists poured money into Dropbox at a $4 billion valuation.

YC has since become a power player in Silicon Valley, helping spawn numerous companies valued at over $1 billion today including Stripe, Airbnb, Instacart and Coinbase. It also backed Twitch, which Amazon acquired in 2014 for about $970 million, and the self-driving tech start-up Cruise, which GM bought in 2016 for over $1 billion.

But in its 13-year history, YC had yet to see any of its companies go public until Dropbox's stock market debut on Friday. Shares of the cloud file storage company surged 36 percent to $28.48 in their first day of trading, giving the company a market value of over $11 billion.