disillusionment

/ˌdɪsɪˈluʒənmənt/
noun
  1. The feeling of disappointment that comes when you discover that something you believed in or admired is not as good, true, or valuable as you thought.
    • The movie explores the disillusionment of young soldiers who go to war expecting glory but find only suffering.
    • His disillusionment with the company grew when he realized they didn't care about their employees.
    • After years of working in politics, she felt a deep disillusionment with the entire system.