disillusionment
n.n. a feeling of being very disappointed or upset because something you believed in is not true. It is like when you find out a person or a plan is not as good as you thought.
n. a state of being disappointed or disillusioned, typically following the discovery that a person or situation is not as good as expected. Often used to describe a loss of faith in an ideal or a political system.
His disillusionment with politics grew after the election.
Many young professionals experience a sense of disillusionment when they realize the corporate world is not as fair as their university professors suggested.
The widespread disillusionment with the government's handling of the crisis led to a significant drop in voter turnout during the subsequent national elections.
From dis- + illusion + -ment.