"A nurse," I said to my pediatrician in response to his what-do-you-want-to-be question. "Because only boys can be doctors." The pediatrician looked at my mom, saying, "And the next time you bring her in, she will have Female Doctor. We can't have our five-year-olds thinking these things!" He also gave her a tape of Mister Rogers Visits the Doctor - in which Mr. Rogers visited a female doctor who happened to be Female Doctor at the practice. From that moment on, I was hooked - I wanted to be a doctor. A kids' doctor.
In third grade, we had to write own what we wanted to be. I said I wanted to be a pediatrician, and so did two of the other girls in my class. We had illusions of running a practice together. Neither of them ended up anywhere near medical school. When I was in high school, I went to a summer program at Brown University called "So You Think You Want To Be A Doctor." It was awesome. We had lectures by different specialists about their fields, got to spend a day shadowing a physician of our choice in the hospital, and got to do some labwork - we saw cadavers, typed our own blood, and learned some basic physical exam stuff.
In college, two of my first-year friends and I were premed and tried to schedule all of our classes together during the first year - I'm the only one who went to medical school - one is in law school, and one is a PhD student in neuroscience. But I never wavered. Somewhere along the line - the summer after my sophomore year - I did some research and really liked it. I met with The Professor, and he suggested the MD/PhD program, putting me in touch with some of his research alums who had done MD/PhD's at various schools. I went with it, although I'm not sure that I was ever truly passionate about the idea. I've realized that I'm pretty good at research - I have decent hands for benchwork and I'm good at coming up with new ways to test ideas - but that I don't love it. What I do love is being on the wards. As much as I dislike finding patients to interview and exam for my refresher course, I love the actual process of doing it. I can't WAIT for third year. I know it's going to be rough, but I think I'm really going to enjoy it.
There probably aren't a ton of people out there who picked their eventual career when they were five years old, but I've wanted to be a doctor since then, and I want to be one now more than ever.