Is there a word or expression for when someone passionately wants something, and then discovers afterwards that it's different from how he imagined?

Is there a word or expression to describe when someone passionately wants something, eventually gets it, and then discovers that it isn't what he thought it was?

For example, suppose that John is a high-school student who admires the football team. He dreams of becoming a football player, thinking of how popular and sexy he would be if only he could be on the team. Then, one day, he is able to join the team, and he immediately regrets his dream because playing football is so much harder than he could have imagined.

For another example, suppose that Kaylee has a life-long dream to visit some exotic land. After years of effort, she saves enough money and makes the right connections to make the trip. Upon her arrival, she is immediately devastated by how primitive the accommodations are and how she has no access to the comforts of life she had taken for granted at home.

Edit: Thanks for the great answers and suggestions. It seems that there are a number of different words and phrases for this, each with somewhat different meaning.

Solution 1:

I would go with disillusionment.

A feeling of disappointment, akin to depression, arising from the realization that something is not what it was expected or believed to be, possibly accompanied by philosophical angst from having one's beliefs challenged.

[Wiktionary]

An example from vocabulary.com:

Disillusionment is when the hard truth of reality makes you lose faith in your dreams and ideals. Like you might have thought your internship at the movie studio would be super glamorous, but you quickly suffered some disillusionment when you realized it involved 14-hour days and lots of coffee runs.

A deep distinction between disillusionment and disappointment from the book "The Poetics of Disappointment: Wordsworth to Ashbery" By Quinney:

Solution 2:

Buyer's Remorse

is the sense of regret after having made a purchase.

"[The] Bears may suffer 'buyer's remorse' over Cutler, but real leaders admit it" -Phil Rosenthal, Chicago Tribune

See also, Caveat emptor; Buyer Beware.

Even if it was the trip of a lifetime, you'd be lucky (though, irresponsible) to not feel a tinge of remorse at having spent your lifesaving's.

Cognitive dissonance

is the mental stress or discomfort experienced by an individual who holds two or more contradictory beliefs, ideas, or values at the same time, or is confronted by new information that conflicts with existing beliefs, ideas, or values.

Aw, man. I thought this was going to be easy.