Pride and the Gloomy Mood
Pride is one root of gloominess; a humble person accepts what comes with a cheerful heart.
Rav Pinchos taught that one root of gloominess is pride. A proud person feels that the world owes him honor, so he is constantly hurt: someone ignored him, someone looked past him, someone did not give him his due. He walks around under a cloud. A humble person accepts everything that comes his way cheerfully, and so his mood stays light. Rav Pinchos was known for living humbly, in a shabby house and with little honor, and his words on this subject come from a man who had worked hard at the very trait he describes. The root of the sadness, he teaches, lies in what we expect, not in what happens.
Source: Medrash Pinchos (ch. 2, the passage on pride and humility, beginning אמר שמרה שחורה)
The next time you feel slighted, pause before the hurt grows. Ask yourself quietly what you were expecting and whether you were owed it. Then name one kindness you received today, however small, and thank the person or thank Hashem. Try this three times this week. You are not pretending the hurt is absent, only choosing a lighter way to hold it, and you may find your mood lifts with it.