Pfeiffer tells us her story

This couple - Ben, who's charming and funny and is played by Bruce Willis, and Katie, who's the needy and complaining one, who I play - represent a lot of contemporary couples. Couples who are in the process of redefining the family and what the roles are of men and women, trying to make a marriage and the raising of children more of a collaboration. I think carving that out is a messy journey.

The question director Rob Reiner asks is, "Can a couple survive 15 years of marriage?" This film is about the ins and out of a relationship. When you see a story about a marriage on the rocks it is usually the result of something huge. But the truth is that most marriages or relationships fall apart because of the day-to-day grind. Our film is a comedy about those tragic little details.

I have a good marriage. When I accepted the job of Katie I was concerned that I wouldn't have experienced enough of the tragic elements to play the part. But with good writing, it's all there - you don't have to kill people to play a murderer or be a president to play the President of the United States. I became the designated driver of the marriage. Between takes Bruce was very much like Ben, always joking and having a good time, while I was the responsible one who had to say, "OK, we have to act now."

In real life I don't have to have everything in place like Katie does, but I think you have to juggle when you split yourself up into many different areas - wife, mother, worker - and I guess the trap is that it starts to define who you are and sometimes doesn't leave time for you to be the irresponsible one. I'm sure we all recognise that in ourselves at some time.