Ewan McGregor and I said this to each other after we saw The Ghost Writer. Every time Roman Polanski did a "No, no, no!," he was right. It was really as if a sculptor was asked to sculpt the embodiment of despair - that was the attitude he would strike. But as with every sort of inspiring teacher you ever had who was strict and scary, when you get it right, the sun comes out, and it's worth it.

My agents were like "Come to L.A., we've got meetings for you." I was like "No, I'm doing this now." Then my father became very ill back in England, and I didn't want to be away. I went back to England and did a bunch of crazy indie movies, all of which I loved with a passion, and none of which did any business.

I thought "I've coped with some crazy situations, and I can do this." But working with Roman Polanski is so different from the fashionable and accepted way of directing now.

I had the best teacher in the business. Kevin Costner was my teacher. I was acting opposite him and he was directing me. The way he directed me, for which I am eternally grateful, is he would watch the scene back on the monitor, which is sort of considered unfashionable - you're not meant to watch yourself. But he was like, "Come around. Watch this. See there, you're doing a great reaction, but you're doing it out of frame." That was exactly what I needed. I learned how to act on film from him.

My parents taught me everything and set me up for life. I owe to them all the things I'm passionate about: music, art, the people I love, my career and family life, the fact that I have children and the way that I raise them.

My very first friend was my stand-in, who's a very dear friend to this day, and she kind of saved my ass. She told me where to stand and where the camera was and where to look. I thought, "If I don't enjoy this, then there's absolutely no point in being an actor."

My parents are both lawyers, and my father always said his best cases have been returns, cases that come into his office from another lawyer. So he said, "Never be ashamed to take a return." All my best roles have happened because someone else dropped out at the last minute, and God bless those actresses for their queeny fits, their sprained ankles, their better job turning up, because that's how I've got my best work.