In my mid-20s, I decided to invest in (and run) two franchised restaurants while also working a corporate career in information security. With close to 25 jobs and a sizeable investment at stake, I learned how to run all aspects of the business effectively, including operations, recruiting, marketing, advertising, finance, and taxes, which turned out to be like a crash-course M.B.A.
That experience helped me understand the basics of building a business and all the disciplines that make one successful.