We have had some good discussions in my workshops about why openings are so hard to get right. The basic trouble is this: We writers need to get the story going (meaning, get into a scene) while at the same time filling in the requisite background information so that our reader can catch up with the characters and with the situation in progress.
This requires us to step in efficiently with our narrators, in summary, to quickly and deftly sneak in the information readers need in order to understand the opening scenes and the forward movement of the story. Generally speaking, you don't want to start with pages and pages of summary narration, or you'll risk losing the reader. At the same time, if you don't adequately ground the reader, he or she is going to be equally lost.
For an example of a writer doing the job right, let's look at the opening of Julia Glass's novel Three Junes. Glass swiftly sets up the situation: Paul, who has just lost his wife Maureen, has joined a vacation tour to Greece. The characters are painted in swift, economical strokes. Here's an example:
The husbands treat him [Paul] as though he were vaguely leprous. Jack finds the whole thing amusing: "Delightful, watching you cringe." Jack is their guide: young and irreverent, thank God. Reverence would send Paul over the edge.
And so, with a strong narrative hand, Glass quickly establishes her characters, and where everyone in the party stands, and by page two we are into the first major scene, where Paul spots a "sunstruck girl with a touch of the brazen," who reminds him of Maureen.
So, to sum up, openings are hard because you are trying to do two contradictory things at once: Introduce background and situation; and move the story forward. It can be done. You just need to be swift and efficient with your narrator, as is Julia Glass in our Three Junes example above.