I was very disappointed by undergrad. I went to a very good, but very large, state school, and all my life I had envisioned college as this small liberal-arts experience with small classes and stimulating intellectual discussion, with everyone in black turtlenecks and being very erudite. Instead I got a lot of "Please make sure you use a number two pencil and fill in the dot completely," alternating with "Chug! Chug! Chug!" It was very fun, but I didn't get the type of learning experience I wanted. I wish someone (my parents, teachers, guidance counselors) had been more assertive about telling me that I'd be happier in a smaller liberal arts school before I left for college.
On top of that I paid my way through school 100%. So many years I was working 40 hours a week and going to school full time. It sucked. So I couldn't wait to be done and out working. In retrospect I probably should have made different choices, and it all turned out okay, so I have no regrets, but I was chomping at the bit to be done almost as soon as I'd started.
I got out into the work world as a corporate drone working not in my field per se, but definitely putting my education to use to some degree every day at work (BA in Linguistics and working as a translation project manager for a language services company), so that was lucky and rewarding. It was nice to actually have money, besides just the $7/hour or whatever wager jobs paid when I was in school. It was awesome not having any deadlines. Actually that's not true, I did have deadlines, but for some reason when I was in the work world it didn't feel like I had any deadlines. I'm not sure why that is but it was great.
What started to wear on me was the stress. More to the point, it was where the stress was coming from. The corporate world is about one thing and one thing only: money. It can be discouraging to gradually discover that the only reason for your existence as a cog in a particular machine is to put more money in other peoples' pockets. To have to do a less-than-stellar job on something simply because your boss isn't willing to pay for the best, because that will eat into his profit margin. So you deliver a translation for a medical device to a client, knowing you put a translator on it who doesn't have medical knowledge, because the qualified medical translator was 3 cents per word more expensive than the translator who specializes in vacation brochures, and your boss was not willing to pay the difference. Then you worry that errors in the translation might cost a life, and you spend your days and nights enraged that (a) your boss is such a greedy bastard to be able to make such decisions and still sleep at night, and (b) you yourself didn't stand up to that, because the last time you did your boss threatened your job, and dammit, rent is due.
I found that I loved my job but I hated the culture around it. So I found another company that shared my value for quality, and it was better. But the sad part is, it's still all about the money. No matter how much you resonate with a company's values, no matter how much they like you as an employee, if the money isn't coming, you could be gone. Nothing personal. It's just the way it is. They've got their rent to pay and so do you.
If you're not careful, you could find yourself taking jobs just for the money, and that can be downright miserable, even if your tastes are simple. Please don't fall into the trap of living an SUV lifestyle and then staying in a miserable soulless job simply to pay for it. You can't take it with you, after all. Even if you are living simply, it can be very hard in my experience to just do a job for the money, "to pay the bills," although many people do it and seem to have no trouble. It's just not me.
I will disagree with lfm, though, and say that having a job you love is not Mostly Awful. It's wonderful. I got out of my first, corporate career, and went back to school to get a teaching license. The second time around for college I went to a small liberal arts college and it was much better. However I was also at a point in my life where college had become simply a series of hoops to jump through to get to a goal. So it was no big deal. I think the first time through college becomes all-consuming for most people: you live and work and study on campus, for the most part, so it becomes your life. Returning students later on can easily tie their studies in to a personal goal, and also usually live and work off-campus and have very full lives outside of school. School is just an "add-on" thing that they do, like aerobics class. So that makes it easier to stomach in some ways, and harder in others (because the sense of "jumping through hoops" can be keener here).
Now that I've been done with college (again) and working for several years, I will say that I love my job. I'm more insulated from the moneygrubbing that was so disheartening in my previous career. I'm still affected by money, of course, but the goal of what I do is not to enable my blowhard boss to afford a new boat. Instead my worth is judged by how well I reach and inspire people, and the difference in my life is substantial. I've been teaching full-time for four years, and my paycheck is *still* a surprise every time I get it. I make way less money than I did before, but it's worth it.
Since I paid my way through school both times, the sense of urgency attached to keeping a job (to ensure the ability to keep a residence) is nothing new to me. It still sucks, being that dependent on it, but for me there wasn't a lot of difference between college and "real life" in that regard.
The important thing to remember is that you can always change, and should. Most people feed you this line about how once you're done with college, your "real life" will begin and you'll ride off into the sunset, and that's a load of crap. You may have to go back to college, or something like it, several times amid the three or four careers you have.