We all set expectations, of ourselves, of others and of the outcome of situations in our lives. So it is very easy to be disappointed when those expectations are not met. What you must remember, is that your happiness is in your own hands, so being unhappy when your hopes and expectations are dashed is your own decision.
For myself, I find that taking some quiet time to examine why I am disappointed solves a lot of these problems. Sometimes my own expectations are set too high, unrealistic even, sometimes the simple acceptance that those expectations are not those of others explains the outcome.
Allowing your expectations of others to be, even in part, the basis of your happiness shows a lack of Wisdom, so learn from the pain, don’t repeat the mistake, and move on. This is, of course, far easier to say than to do. But to help maintain your happiness, set realistic expectations for yourself and accept that failing to meet those expectations does not mean failing completely.
The Search For Enlightenment 
Jan 09, 2012 @ 00:39:10
in business, we call that “root cause analysis. In Buddhism, we call it “self reflection”. =)
Mar 27, 2012 @ 01:00:31
Letting go of others’ expectations of us and really honoring our own is, I think, half the battle. It’s easy to get wrapped up in others’ desires, narratives, and beliefs about what we do, how we do, and why we should do. But, just allowing whatever has manifested to be – expectation met or unmet- has value. Sitting in the squirm of discomfort is, in itself, highly valuable. Thanks for another thought- provoking post.