Appointment and Disappointment
The mismatch between expectation and reality results in 'disappointment." We have an appointment, it gets "dissed", and we get "dis-appointment."
We can recognise a number of key pieces in the Disappointment Process.
First you need a detailed image of how things will be, or should be, or ought to be.
Then you have to spend some time developing this image, making it more idealistic and practically living in it.
Finally you compare the reality with your fantasy and become upset because they do not match!
Of course, this only produces a somewhat mild state of disappointment. To experience REAL disappointment - the kind that leads to either depression or anger - you have to then spend some time berating the fact that the two images do not match, and generally blaming yourself and/or other people for this disappointment!