Thomas Hardy said "The sudden disappointment of a hope leaves a scar which the ultimate fulfillment of that hope never entirely removes" This is so much truer of the hopes one has from a loved one often in-articulated but with a latent expectation of fulfillment all the same. So they may do a hundred other things right but fail to fulfill that one thing much hoped for. Rationally, one would expect to let go of the disappointment and rejoice over all that was done right. It was interesting to read this article which explains why the obviously rational choice does not always get made
Usually it is assumed that people who value happiness are able to hold on to positive feelings and may be resilient, if not immune, to the negative effects of disappointing experiences. But this may not always be the case, according to the findings of a recent study. Under certain circumstances, valuing happiness may be self-defeating and result in disappointment, depending upon how people evaluate their progress toward that goal
And for those of us carrying bad relationship baggage from the past a simple disappointment can feel like a deep betrayal. A symptom I am very familiar with but did not fully understand.
They misinterpret the anxiety signals that occur with - or immediately before - feelings of disappointment. Instead of a mere signal of imminent change, the sudden rise in anxiety, though relatively minor, seems to signal disaster. The resulting surge of adrenalin amplifies the disappointment and makes it seem like trust-destroying betrayal.