Alfonso Cuarón's tense space adventure was a huge box-office success in 2013, and went on to win several major Academy Awards shortly thereafter. However, in the earliest days of development, the studio was hesitant to proceed with the film because they thought that a female-led action movie would be a tough sell for audiences.
Seemingly forgetting that characters like Ellen Ripley and Sarah Connor had been kicking ass for decades, Warner Bros was concerned that Gravity would be a financial failure because it had a female lead, and according to THR, they wanted to give it a stripped-back budget as a result:
"...budget was on everyone's mind given that, historically, female-driven action films have been a hard sell."
The only thing that managed to somewhat dampen this fear of failure was the fact that Angelina Jolie was "loosely" attached to star. But when she dropped out, those studio worries resurfaced once again.
In fact, Warner Bros had persistent nerves about the film all the way up until Comic-Con 2013, just a few short months before it was due to release. During the convention, the film's opening sequence was screened, and received an incredibly enthusiastic response from those in attendance, calming studio fears in the process.