Scarlett Johansson "always" feels "unsure" of herself when she takes on a new role.
The 'Avengers Assemble' actress believes actors get "lazy" if they go into a job with a preconceived idea of how they are going to play a part, and the blonde beauty thinks the "fun part" is working out the best way to portray a character.
She said: "I always feel it's good to be unsure of myself as an actor, otherwise you get lazy. You have to believe that you can do it and that you're the right person for the job, but I think it's good to not always know how you're going to do it. The fun part is figuring it out."
The 27-year-old star - who plays superhero Black Widow/Natasha Romanoff in 'Avengers Assemble' - is pleased to be portraying "more dynamic characters" as she gets older, but she still enjoys discovering new characteristics in every new role.
She added to the Daily Mirror newspaper: "As an actress you're always training to either lose weight, put on weight or change your body. But since I wasn't an athlete growing up I was never aware of what I could be capable of. It's kind of fun to discover that.
"I was very fortunate when I was a bit younger to be the ingénue and to play characters that were very much in transition. I was in transition in my life as well, being a young woman. I feel that I'm now moving into a phase where I'll be playing more dynamic characters... grown women."