Executive summary: my general direction was clear at the end of high school, but my specific career path didn't reveal itself until the end of graduate school (Ph.D.).
I was a kid in the 1960s, the heyday of the "space race", which got me interested in astronomy and the other physical sciences. I followed the space flights, tinkered with a chemistry set in my basement, and read about physics. When I graduated from high school, I was undecided between chemistry and physics, but it was clear that I wanted to do something in the physical sciences.
Towards the end of my freshman year in college I settled on physics. I wasn't aiming to become the next Einstein or Heisenberg, and get my name attached to a famous equation or theory. I simply enjoyed studying the stuff and tinkering around in the labs at night, and hoped I would be good (and lucky) enough that someone would be willing to pay me to keep on doing it. And so I went on to graduate school, which paid me via teaching and research assistantships.
I made it all the way through grad school, but at the end, I had a career crisis. Although I had enjoyed life as a grad student, participating in research and getting my name on several papers as part of a large research group, I decided I really didn't have the temperament or desire for an academic research career: a series of postdocs followed by (if I was lucky) a tenure-track position at a research-oriented university, in a research field that didn't have a whole lot of long-term positions available, and having to chase research funding continuously, develop proposals for new experiments, etc. I'm just not an entrepreneurial sort of person. (For the same reason, I've never ever been tempted to own and manage real estate.
Two alternative possibilities stood out. First, my day-to-day work had been mostly programming. I was entirely self-taught except for a couple of FORTRAN courses as an undergraduate, but I enjoyed it, and my colleagues seemed to think I was good at it. Some of the previous grad students in my research group (and other similar groups) had gone into programming careers. So I could very well have taken that route, and probably had a satisfying career.
Instead, I decided to try to recapture my undergraduate days at a small college, by becoming a professor at a similar school which focused mainly on teaching. I got lucky and ended up with first a two-year stint at one school as a sabbatical replacement, then a tenure-track position at another school from which I'm now retired.
My investing princiPLEs do not include absolutely preserving princiPAL.