EXCLUSIVE: Jennifer Garner says her new movie explores people's 'desire to drop out of their own lives'

There's a simple reason why Jennifer Garner agreed to the role of Diana in the upcoming movie Wakefield. It spoke to her.

ET caught up with the 45-year-old actress on Thursday at the film's premiere in New York City, and she explained why she thinks Wakefield will resonate with audiences. In the movie, Bryan Cranston plays a man, Howard Wakefield, who has a nervous breakdown, and leaves his wife (Garner) to go live in his attic for several months.

"I think anyone can imagine just the desire to drop out of their own lives," Garner noted. "It's just to actually do it, to follow through and to live outside of your life [while] watching your own life for a year, [that] is pretty out there."

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Garner -- who looked stunning at the premiere in a strapless black and gold dress -- also praised Cranston for his performance in the film, calling him "the most fun."

"He's such a goofball and he went through so much making this movie," she recalled. "He was constantly putting a beard on, putting dirty nails on, he got skinnier and skinnier all the time. I don't know why I work with these guys who are all getting skinny! But whatever, he did, he really went through it."

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See photos of Jennifer Garner and Ben Affleck together:

Wakefield hits theaters on May 19.

Garner has been going through some changes in her own life, as she and husband Ben Affleck filed for divorce last month. Here is ET's look back at their relationship and two-year separation:

Reporting by Darla Murray.