We experience expectation of future events. I suppose the mind integrates information from the present and associated memories from the past to generate expectations. This ability promotes survival. When future events turn out to be different from expected, the mind has to do the work of reimagining a new future and ways to negotiate it. We experience this gap between reality and expectation as frustration, anxiety, stress, fear or any of the other negative emotions. Perhaps the value of the negative emotion is to induce one to seek remedies for the failed event. I imagine that we may not be motivated to seek remedies if the failure did not cause us a negative emotion.
Negative emotions drives one into a fight or flee mode where rationality is overridden. A better way to deal with failed expectation is to simply adjust the expectation, remember that there is no way but to close the gap between expectation and reality - check if the gap can be closed by communication, what was ignored or not understood at the time of experiencing the expectation. Every confrontation with a negative emotion is a time to adjust expectation. Such a practice should make one skillful at negotiating unexpected turn of events.
