Expectation is a multi-pronged weapon that spears everyone, even the wielder. It is both the anticipation and the result, often against the will of those for whom it is their stock in trade. When writing you can use expectation to excite the reader and give them what they want. You can surprise them by working against expectation. A third consideration that may come less often is that you can play with expectations within the story from the perspective of different characters.Two characters can have two different expectations of the results of some event or the result of specific conditions being met. They can be played off of each other for more tension.
Also, though, one can have the other kind of expectation which is to see the result in a certain light that isn't necessarily true either due to the bias of the expectant person or because they did not think it through. Expectation as a point of conflict can, as you'd expect, occur both before and after situations have completed. Misunderstandings and sticking by false conclusion work here as well.
Be aware that parallels drawn between expectations and morals create points of division in the readership as well as at a fiction/character level. You can't expect every outcome, but try to avoid fallacies that can be damaging to the result you desire with your work. The same is true when you are advertising, and when you represent your work everywhere, which is what we all do all of the time we're in the public eye and the social networks.
Music: When The Wild Wind Blows by Iron Maiden. Or get MP3s.