Which of your jobs offered surprising lessons?

Over the last year I have been working as a resume writer. I interact with mid to senior level professionals across a wide array of industries. Every week, I learn something surprising about the way our world works: this week I interacted with a man who sources the canola seed to make our canola oil. A few months ago, I was working with a man responsible for marketing what became a teen-fad movie series. I thought this would just be a placeholder job while I worked from home after having my first kid, but instead I find that I am learning the ins and outs of multiple industries and professional roles. What jobs have you taken that yielded surprising lessons? Did those come in handy later?