I'm not sure why. But I can often tell whether I'm going to like a film just from watching the trailer. In fact, I can't remember the last time I liked a film, whose trailer I disliked or vice versa. This does require you to know that trailers often warp the true tone of film in a effort to appeal to the largest demographic of people possible. Quite often dramas are made to look like thrillers. Or deliberately dramatic editing techniques are employed to make a particularly moody, slow-paced film look like a rollercoaster. But generally, just from snatches of dialogue or images, I can decide what films I will like at almost 100% accuracy. This is why I feel comfortable buying a film sight-unseen, as long as I've seen the trailer and liked it. On occasion, I buy a DVD, knowing nothing about it, and only then, have I been disappointed. Examples of disappointment: Legally Blonde, Deep Blue Sea, Charlie's Angels, Moulin Rouge.