The word "disappointment" refers to the way that we feel when things do not turn out like we had hoped. Deep disappointments in life would be things that are really important to us and that do not turn out the way we hoped. A small disappointment would be something like going to an ice cream parlor and finding out they were out of your favorite flavor. A deep disappointment in life would be much more serious. It would be like never getting a job that you liked. Or it might be something like having your kids get expelled from high school. These are things that would make you seriously sad because your most important hopes did not come true.
It think disappointment is such a feeling that ought to be felt as "deep" if someone wants to come up to the surface again"Disappointment, defeat, and despair are the tools God uses to show us the way.” Paulo Coelho