Lulu Wang on Awkwafina's dramatic turn in "The Farewell": "I didn't know she had that in her"

Director Lulu Wang on new film "The Farewell"

The new film "The Farewell" tells the story of a family coping with the news their grandmother has terminal cancer. They decide not to tell her and stage a wedding in China as an excuse to visit her and say goodbye. The movie was the breakout hit of the Sundance Film Festival this year, earning its writer-director, Lulu Wang, the festival's Vanguard Award.

In her first dramatic role, comedian and rapper Awkwafina plays Billi, her granddaughter, who was raised in the U.S. and struggles with keeping the secret.

"She sent an audition tape in and when I saw the audition tape, I was blown away. I didn't know she had that in her," Wang told "CBS This Morning." "When I first met with her, I was pretty surprised that she wanted to do this. I thought, 'you're a rapper from Queens, why did this resonate with you?' She said she was raised by her Chinese grandmother because her mother passed away when she was 4. And just really connected with the relationship between Billi and her grandmother."

One of the central themes of the film is the idea of the collective good versus the individual good and how two cultures see them very differently.  

"Awkwafina's character, Billi, as an American, she very much believes in truth and freedom as the most important values, and her Chinese family says, well, are those really good values if it doesn't really serve the person you're telling the truth to? If it doesn't serve the family? It's also this sense of duty that if she tells the grandmother the truth, she's not the person who's going to be around to deal with the results of that truth being told," Wang said. I

The story is based on a real lie that was told in Wang's own family.  

"My mother called me to tell me that my grandmother was diagnosed with terminal cancer and we weren't going to tell her and if we wanted to go back to see her, it was under the ruse of a wedding for my cousin."