I love learning, and couldn't decide on a single major. First I was planning on CS / Math, but wound up taking a physics course, asking the right questions, and the professor hired me to do research for him and put me on the honors track. As long as I was matriculated as a physics major, I had a scholarship and a pay check waiting. I also happened to love it. Because my University didn't allow more than two courses to overlap between majors, I wound up taking enough math courses to otherwise have majored in it, but it didn't count.
In my senior year, I took philosophy to satisfy a writing requirement. It was analytical philosophy. Logic and reason was valued above all. We discussed the problem of other minds, philosophy of religion, and a broad array of other things I had always pondered. In fact, I thought I must have been the only kid in kindergarten wondering how I could be certain that my parents were actually conscious beings and not just bags of molecules. How could I know for certain that they had a mind and consciousness in the same way that I did? When I found out that you could get paid to think about these things and teach people how to think, I was hooked. I decided to double major, and spent an extra year filling all of the requirements.
After graduating (the first time) I spent 6 months working at a local bookstore, deciding what track I wanted my life to take. I could teach high school physics, I could get a PhD in physics (though I was getting tired of seeing divs, grads, and curls every time I closed my eyes). I could become a philosophy PhD and later professor, which sounded like a dream job, but was difficult in practice to obtain.
Then it occurred to me that I didn't know much about biology and my own body. I would be stuck with it for the rest of my life, so I thought maybe I'd go to medical school. The problem was two-fold. I didn't meet the pre-requisite coursework for applying, and my grades were not competitive (I never handed-in homework. I studied things for their own sake and not for the grades.)
After watching a few UC Berkeley lectures on chemistry and biology, I decided I loved biology. I returned to my University to get a degree in some form of biology. I wanted to learn it very well, get great grades, and I chose the hardest sub-discipline with the fewest students: molecular biology and biochemistry.
I was amazed to discover that when I actually tried and cared, I was at the top of every class. I graduated again, with a 4.0 and applied to medical school.
Amazingly, even with these credentials, a large body of research, and a very competitive MCAT score I was still only accepted to a few schools.
I wound up getting into a combined MD/PhD program, which was an additional 3 years over regular medical school, but allowed me to conduct research. It also came with full tuition and a stipend.
I'm now in my third year and doing research at the NIH. I have five more years until I graduate for the final time.
In retrospect, I could have forgone almost all of college and just audited the courses that interested me. In fact, I believe that college is of only marginal value to most people. Most of the skill set I acquired I learned in high school, on my own, with books and computers.
Without college, however, I would never have gotten into medical school. It is definitely necessary for some things.
If you're studying four subjects in your final year, how do you go into any depth in them?