When you experience discontent, you're not happy. You've been let down — either by others or by yourself.
The word discontent is made up of dis, meaning "not," and content, "a state of peaceful happiness." So as an adjective, discontent means "not happy or peaceful," like the discontent Egyptian citizens who expressed their dissatisfaction with their country's leader by protesting and demanding he give up power. As a verb, discontent means "to make unhappy," like bad news that discontents you.