The thoughts and hopes that go through ones mind before an engagement/party/happening etc. that consist of imagining what it might be like.
The equation to find satisfaction is found by taking enjoyment and subtracting expectation from it. This is to say that one should never expect too much from something.
Ben expected the party to go perfectly as planned. However, the band did not turn up, the drinks table was knocked over, three men were taking to hospital for the consumption of too much whisky an his car broke down on the way back. Although Ben had had a great time there, he found that he was not satisfied with the outcome because he had had very high expectations.