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.Read more at Entertainment Tonight