The Shame star revealed that her penchant for starring in independent films early in her career meant that she was not often recognisable in public, as many people had not seen her work.
In an interview with Little White Lies, Mulligan explained: "I don't know, it's funny. I used to tell people that I was a geography student until I was, like, 23, because I'd say actress and they'd be like, 'Oh, what have you been in?' And I'd be like, 'You won't have seen it'.
"It was just so awkward and I hate that at Customs because I'd say 'Never Let Me Go', and they're like, 'Pfft!' Because they demand that you tell them because they're like, 'Oh, you're an actress. What have you been in?' You're like, 'You won't have seen it.' They say, 'Go on!' You say, 'They're chick flicks, you really won't have seen it'. It's awkward. I think because I didn't train, I've always felt kind of quite unqualified."
However, Mulligan insisted that pursuing her passion is not always easy, recalling: "I guess I make a living from being an actress and it is always what I've wanted to be, but there are days when I'm just terrible and I can't act. Like, there was a day in Never Let Me Go… There was a whole scene where I'm facing down the beach while Keira [Knightley] gives us a little note.
"It's a very serious scene and me and Andrew [Garfield] are meant to react emotionally. I couldn't do anything that day. I couldn't do anything. I just turned away. It looks like I'm having a moment but I'm just not… I can't think what to do. Sometimes when that happens I think, 'What on earth am I doing?' I think the most confident I feel as an actress is when I'm doing theatre."
Watch Carey Mulligan talking about her forthcoming role in The Great Gatsby with Digital Spy below: