I was maybe 14 or 15 when I saw East of Eden, the 1955 film based on John Steinbeck's novel. It uses an important moment in American history, the first world war, as the backdrop to a tale about two warring brothers, drawing on the story of Cain and Abel. Though I've since seen films that were much better, this was the most intense cinema experience that I've ever had.

I had a rash so I wanted to hide in the cinema to avoid being seen for a while by a boy I was in love with, my first love. Hiding from him, I went with a friend to the biggest cinema we had in Denmark. We saw East of Eden and cried throughout. When I walked out of the theatre I was still filled with all this emotion... and I saw my first love standing outside! I think he had called my parents to figure out where I was. Then my friend discreetly took off, and after that the boy and I became boyfriend and girlfriend and were together for a couple of years.

People involved in serious accidents often say they were surprised at how sensibly they were able to react in a crisis and how everything seemed to move in slow-motion, so they could recall all the details. On that Sunday afternoon, East of Eden did the same thing to me emotionally. I understood what love could be and what films could do to you. It was almost as if that was the day I became an adult.

There was a scene where Cal, played by James Dean, and Abra, played by Julie Harris, are on a ferris wheel. She is engaged to his brother, Aron, but in that scene Cal declares his love for her. He is completely embarrassed and knows he should never have done it; meanwhile she experiences a huge conflict of loyalty. And they're stuck on the ferris wheel, in the middle of the night, up in the air!

Obviously it's shot quite simply because the camera can only be in so many places when they're sitting on their little ferris-wheel seat, but the acting, the chemistry, the attention to detail in that scene is almost unsurpassable. It's so well directed and so pure. Though East of Eden is very emotional, I honestly don't think it veers into the sentimental because it's authentic. The characters are experiencing these feelings for the first time, and probably as actors they are too. You often see a certain innocence in the acting in the film, which is a rare thing, I think.

Years later, now that I'm a film director, I haven't been tempted to look back at it: it felt like it belonged to that specific time of my life. But now that I am thinking about it I have to see it again soon, and I have to make sure my 17-year-old daughter sees it… even though she insists she doesn't want to see any films that are older than she is.

One Day, starring Anne Hathaway and directed by Lone Scherfig, is out now on DVD