Michelle Williams finds work difficult

London: Actress Michelle Williams says she always finds working on film sets a little difficult.

The Oscar-nominated actress has taken on her biggest role till date as Marilyn Monroe in "My Week with Marilyn", reports femalefirst.co.uk. "It is the most challenging role I`ve taken, and I think it always will be. There is a degree of difficulty that always exists for me at work, but this really stepped it up. I was nervous, of course, but I tried not to think of her as an icon," she said. IANS