Emma Watson "almost broke down in tears" when she was asked to act angrily.
The 'Harry Potter' actress - who has played Hermione Granger in the school boy wizard franchise since 2001 - found it "scary" trying to portray characters in a "powerful" and "sexy" way after taking up acting classes at university.
She told Britain's Harper's Bazaar magazine: "My acting tutor said the hardest thing for me was to get angry. I almost broke down in tears when they tried to get me to be angry. I said, 'I can't do it, I just can't do it.'
"I keep all of that really bottled up somewhere and I feel unleashing it would be the scariest thing - and to let myself be powerful, sexy, all those things, it's scary for me. Even playing the bad girl in this shoot felt a bit uncomfortable and awkward, it didn't come naturally at all."
Emma, 21, recently quit her English course at America's Brown University in April after finding it tough to juggle her film, modelling and promotional work.
Asked why she did not choose to enrol at an English university before moving to the States, she said: "I felt suddenly very claustrophobic...I thought, 'I can't stay here, I won't be able to concentrate, I won't be left alone.'"
But it was recently reported Emma - who plans to enrol in other education institution later this year - could choose England's Oxford University to carry on her studies.
In April, she wrote on her website: "Recently I've had so much to juggle that being a student AND fulfilling my other commitments has become a little impossible.
"I've decided to take a bit of time off to completely finish my work on 'Harry Potter' and to focus on my other projects."