WARNING: I pulled a bangali and this suddenly became very, very long, very unintentionally. Sorry about that. >.>;This is actually a really interesting question - and I know for some people the answer can be pretty mundane (I know someone who originally enrolled in my current degree because she thought the name sounded funny!), but definitely not in my case!
I actually had a lot of trouble picking a career or uni pathway - for ages I wanted to be a writer, then I thought I might like to act, then I wanted to be a musician, then I wanted to be a teacher, until recently when I decided I wanted to become a scientist. Even now, all of those things are still a part of my life - I don't write much anymore, but I did do imaginative for context back in the day, and it was easily my best scoring SACs. I still occasionally do theatre stuff (mainly just appreciation now as opposed to acting, but I did do musicals in high school), and still bust out the old bass and play some music, and teaching comes through when I tutor/doing work for the AN gods/helping out on the forums here.
The interesting thing is I never liked maths or science - I had always been good at them (I can remember one trig test where I didn't even attempt the last question because I couldn't be bothered and knew that I had already passed - my teacher was really upset with me that day, hah), but nobody had challenged me to be interested in them. Then, something happened in year 10 - it wasn't academic stuff that got in the way, but it still meant that I spoke to the principal and made the decision (against everyone's wishes, who saw my academic scores and thought I would be making another mistake) to stay back a year. Easily the best decision I have made in my life - ever.
When I repeated, because I was smart and got bored with maths class, I asked that they still let me continue on to year 11 GMA. The school was fine with this, because it wasn't uncommon for year 10s to take GMA (in fact, at the time, most of the class were year 10s). When I was being intellectually challenged, I really started to shine, and I trumped the class for the whole semester. At the time, I still didn't like science, but I had made some friends. This is important to the story.
What really sparked change was when I went into second semester - due to the massive subject change for the second half of year 10 (that's just what my school did), I had to move maths classes, and I got the other maths teacher. This woman was spectacular - as a teacher, she was pretty normal. She wasn't the best at teaching content, but she knew her stuff, and managed to leave us with no doubts in our mind. What REALLY made her shine was that she didn't teach maths - we lived it, and we just happened to be in the classroom. It was a very profound moment, and the way she'd talk about maths made me honestly want to explore it more. Before then, I didn't even plan on doing year 12 maths, and I was going to replace it with literature at the end of year 11. That class, however, made me seriously consider taking specialist maths in year 12.
Finally, after that, came subject selections. At the time, my experiences with my maths teacher brought my whole enrolment into question. I suddenly had no idea what to do, and ended up talking to my friend from that science class I mentioned. She said to me, "do chemistry, I don't have any friends for it", so I signed up for chem. At the time, I had no interest in science at all, let alone one of the "harder" sciences - but I had no idea what else I would put there, and at least this way I'd have a friend.
Then came the first two months of year 11 - and holy hell chemistry was my favourite class. Methods was really "eh", nothing like GMA which I had loved, but chemistry easily made up for it. I regularly topped my class - no longer was I just "smart" and got good grades, I got spectacular grades because I was "interested". Funnily enough, people always saw me as the smart person because of this, but I never got any academic awards for whatever reason - I digress, though.
It was after this that my care group teacher told me about something called the "National Youth Science Forum". At this point, I was so in love with chemistry, and the program seemed mildly interesting, so I applied on a whim. I later found out that applying meant hours and hours and hours of work just to be considered, but I endured and eventually got accepted into the program. This is the second best thing I've ever done for my life.
After attending the program (note: if you're currently in year 11 and like science, DO THIS PROGRAM. ty), my eyes were opened. As a part of the application, I had to tell them what uni degree I planned on doing, so I told them something random that I didn't particularly care about. However, attending the program taught me something - scientists are people. It was something I never really though of before - constantly looking at degrees, trying to find something with chemistry but no biology (hadn't done bio since year 7 nor was I tempted to pick it up), and my careers councillor's best job pick was med (lolwut?).
But NYSF had made me realise that I could be a scientist - it wouldn't be an easy path, but my logic was that in this world, there will be scientists out there, and what's stopping me from being one of them if they're going to exist anyway?
So, I looked around a lot of unis, but nothing having a lot of money and realising I'd have to survive off of Centrelink and scholarships (and then realising I didn't have enough drive to work hard enough for a scholarship in about term 4), I decided to look locally. From there, I decided that Monash's travel time wasn't too large to make me go mad, I liked the facilities and their course looked good and like it would take me straight to being a scientist as soon as possible. (fun fact: it does do that!)
Things got interesting from there, because things didn't stop at all.

In particular, take home message before I continue:
So far, my story makes it sound like I had my career chosen before year 12 even started and have been following through ever since. This is not true - I had decided where I wanted my career to be (in science and research), but I wasn't even close to deciding what I wanted to do.Going into uni, I wanted to do research into natural hazards - things like landslides, avalanches, what causes them, etc. I was also taking maths, because I still loved maths (particularly after year 12 specialist), and had decided to pick up physics because I had never done it before. This left one more subject I had to decide on, but the problem was that I didn't like the sound of anything. I could try bio, but I felt very unsure about it, and decided not to. Picking up another maths didn't seem like a good idea at the time. I nearly took philosophy (even asked brenden here about what the subject was like!!), but eventually decided to give chemistry another try. At the time, I was shocking at chemistry, and only managed to get a decent score because I still scored higher than most of my cohort with our rank 1 being absolutely excellent and because the exam was particularly easy that year (anyone seen the 2013 chem exam? Ahhh, it was beautiful). See, year 12 had made me DESPISE the very subject that got me interested in chemistry, so making this decision was hard.
Fast forward to the end of the first semester. I had continued to love maths, even moreso now, and decided that I hated physics and chemistry. So, since I had really enjoyed probability in 3/4 methods (it was my favourite AoS... Which wasn't too hard seeing how much I didn't like methods, but still), I decided to pick up a second year probability unit, because being in my course meant that I could do that. Then, to replace chemistry, I decided to pick up statistics, thinking I could use it to teach further (fun fact: lolnup. It does mean I can tutor the new methods and specialist stuff, though!). This is where bits get tricky, though - after my first semester in geology, a particularly lousy lecturer made me despise the unit, and I no longer wanted to continue on to natural hazards. However, my chemistry lecturers had all been fantastic (anyone here know Chris Thompson?), and I had actually enjoyed chem that semester - even though I was still shockingly bad at most of it, good work during semester and the exams being similar to the practice exams meant I nearly got a HD in it! So, I dropped geo and continued on with chem.
I had, of course, entertained the idea of doing nothing but chemistry subjects - however, I needed to complete a minor for my course, so I decided to minor in chem.
This decision eventually changed this year - I really loved my 3 maths 1 chem semester, and it just cemented my wanting to do maths, but it did make me want to consider chem more, so I applied for a research project in chem to open up my options and give me the ability to major in chemistry. After this year, I decided that I liked lower levels of maths, and like applying those lower levels to my science subjects - however, I didn't have the drive, motivation or intelligence to push further into research, and that was my end goal. However, the project I did for chem taught me the opposite - thanks to my work in maths, I realised that I had developed the logical reasoning, critical thinking and the general ability to do chemistry research, and I flat out just enjoyed chem research a lot more than I enjoyed maths research.
Which brings us to the present day. At the moment, I'm now in the middle of a research project, just finished the research project from last year that I mentioned (including a 20 page thesis. Do not spend 1 week writing something like that, for the love of God), and have another project lined up for when semester begins. At the end of this year, I'll be moving into honours in (hopefully) supramolecular and fluorescent chemistry. In the mean time, I'm also helping out AN with things such as note writing, lecturing, making lectures happen, other odd jobs, etc. and absolutely loving the work!
man that was long plz don't hurt yourself because you're spending ages reading it .__.