Writing a letter can change the course of history - or in this case, the course of a film and the course of the life of a very public, much-loved star.
Meryl Streep never dreamed she'd be offered the lead role in Mamma Mia! Actually, back in 2001, after 9/11, she took her daughter and some friends to the Broadway version hoping to find a measure of relief from the then-recent tragedy.
Streep told John Hiscock of the Telegraph: "We left floating on air. We were so elated. It couldn't have been a better tonic for the city and I wrote the cast a note thanking them for the music and what they gave us because it was something that meant a lot at that point. It was a gift not just to my little girl and her dispirited friends but it was a gift to the whole city.
"I never imagined the cast would make copies of the letter and send it to England and everybody would have it on their refrigerators, which I was told much later is what happened."
That note was remembered seven years on when director Phyllida Lloyd and her team contacted Streep and asked her to play the role of Donna in the film version of Mamma Mia!
The casting of Meryl Streep was an extremely smart move that helped Mamma Mia! have the largest weekend opening of any movie musical to date.