Life has its ups and downs. Things will not always go as expected. Expectations cultivate sadness, and disappointment when life doesn’t go as planned. Although articles mention the way to combat disappointment is to not have expectations. I find that a bit unrealistic, as expectations are part of our human nature.
What you can do is take on those feelings of sadness and disappointment, and be aware that these feelings will eventually fade. Emotions never last. Take it on as a lesson that life doesn’t always go according to your plans. There will be hiccups, but there can always be lessons to be learned from it. If you think others disappoint you, remember that it is coming from your expectations of them, not from them. No one owes you anything. It is normal to expect things, but one must be aware that life is ever changing and unpredictable. This can help one deal with disruptions along the way.
Psychology of Mindfulness 