This sort of happened to me. I wanted to do software. I had an idea in my head what that would be like. I started my bachelor of computer science degree just before the iPhone came out. Facebook was still new and novel.
When I finished it was all smartphone apps, web 2.0, open offices and agile assembly lines. Gone is the dream of working in a private or semi private office, hell even cubicles seem unlikely these days. Gone is the dream of going to work and solving novel problems, instead most of what I do is data plumbing.
Maybe the software world was never what I thought it was. Maybe it was on some level always this way. Maybe my dreams were bullshit from the start.
Either way, my dreams about my future didn't exactly pan out the way I wanted.