If I start watching a film, I always finish, no matter how dreadful it might be. Here's why:

1) I've paid to see the film.

2) I write reviews of every film I see in the cinema, and cannot do so with integrity if I walk out before it finishes.

3) I also write novels and short stories. The study of bad storytelling is humbling and illuminating. Studying what doesn't work is frequently more instructive than the study of what does work.

The closest I've ever come to walking out of a film was Institute Benjamenta (a much critically acclaimed film, I might add). It's a strange, Lynchian tale about a servants finishing school, but quite honestly I found it unbearably dull. The cinema where I saw it in the mid 1990s (Harbour Lights Cinema, Southampton) usually had an usher sit in during the film. I knew the ushers well (I was a regular attendee - great cinema) and they told me this was the first film they'd ever had ushers sit in for ten minute shifts, as it was so dreadful.