The 35-year-old star - who is currently expecting her first child with partner Guillaume Canet - claims her profession allows her to study people closely, which she feels is important as she has always questioned the purpose of her life.
She said: "I think being an actor is kind of an anthropologist. Actors study human soul, human heart, human behaviours. We try to understand this in order to be able to be true to life.
"And when I was a teenager I was kind of special. I was very scared of other people. So I would hide. But I was more dark.
"I started to ask myself very early while I was here. And I think it makes your innocence go away faster, to have this obsession of getting an answer about what you are doing here."
Marion won an Academy Award in 2008 for her portrayal of iconic singer Edth Piaf in `La Vie En Rose` and she admits she felt "haunted" by the character for a long time after finishing the movie.
She explained to Observer New Review magazine: "I had this weird feeling - and I`m very sane! I don`t live with my roles, I`m a really normal person.
"But I couldn`t let her go because her biggest fear when she was alive was to be alone.
"And then when we finished the movie, I didn`t want Edith to be alone. That`s crazy! Then suddenly, going back to my life and leaving her alone- It just took a while for me to realise that she had been dead for a while. So it was OK, she was not alone, she was gone."