They may lack perspective or even wisdom, but there's nothing wrong with a 17 or 18 year old having a 'dream' school. My daughter got into hers, but we can't afford to send her there. It's a very good but not tippy-top school, and maybe even a bit obscure, but it was right up her alley. She is bummed out, but also reasonable, and is well aware that there are pluses and minuses to every college, so she is moving on.
Anyway, the world would also be a boring place if everyone wanted the same flavor. If they have a dream, or work a little harder for the hope of getting the sundae with the cherry on top, then so be it. We learn all the time as we go through life.