noun

disappointment resulting from the discovery that something is not as good as one believed it to be.

the old enthusiasm for the government evaporated into a more cynical disillusion

disenchantment,disillusionment,disappointment,disaffection,dissatisfaction,a rude awakening

verb

cause (someone) to realize that a belief they hold is false.

if they think we have a magic formula to solve the problem, don’t disillusion them

disabuse,undeceive,enlighten,set straight,open someone’s eyes,disenchant,shatter someone’s illusions,disappoint,make sadder and wiser,throw cold water on