The difference between expectations and reality is disappointment (and sometime annoyance/anger).
So when you are feeling disappointed, take a step back and ask the following questions:
1. Were my expectations too high (am I the problem … which is typical the root cause)
2. Were the situations not what I expect (was my original view/assumptions wrong)?
3. Did the other party try?
4. Did the other party even KNOW the expectations?
5. Did the other party have the same standards?
6. Could I have done something so the other party could’ve met the expectation (aka communicate)