20 HUGE Hit Movies NOBODY Saw Coming

3. Once

It would've surprised not a single soul if a $150,000 Irish musical rom-com starring people you've never heard of came and went in a blink, and yet John Carney's 2007 film Once became a modest event in its own right.

After premiering at Sundance to rave reviews, it performed extremely well on limited release, ultimately grossing $23.3 million globally. 

While not a historic box office performance compared to some entries on this list, relative to its budget and the non-existent profile of its filmmaker and cast, it was an astonishing result all the same.

The film's success was undeniably aided by the chemistry of leads Glen Hansard and Markéta Irglová, and the absurdly catchy title song "Falling Slowly," which went on to win the Oscar for Best Original Song.

This led to Once being adapted into its own hit stage musical - an outcome it's tough to imagine the cast or crew ever considering when they were making it.