Yep, being my mother's primary caregiver for the last four years of her life caused me to memorize medications (and their interactions), vitals, meals, therapies, CNA knowledge, RN knowledge and plenty of MD knowledge. Never in my life did I want to know about health care. It was always something others did to me. But, it was fascinating after I got into some of its practices. The real providers considered me their own little Dr. Shaun Murphy because I helped with everything, and often offered advice to make their work a little more efficient (based on my systemization skills). In other medical settings (clinics and hospitals), I was well known for challenging MDs and RNs about their presumptions, and demanding that they do their jobs correctly; again, I would advise.
In college, I rebuilt my Volkswagen Beetle's engine. Very useful knowledge about vehicles came with that task.
On a whim in high school, I sign up for a Foods (cooking) class for two years. Absolutely the best unintended knowledge came from that experience. The instructor taught the class to cook by knowing food chemistry. Once I understood her, I no longer needed recipes. I could cook by understanding the chemistry.
I guess I have had many such experiences.