I didn't think of it as an investment at the time, but cutting most of my last two years of high school to learn programming 24/7 paid off with a lucrative career. I managed to graduate and get a HS diploma despite rarely showing up. I borrowed $2,000 from my grandparents to buy an ADM-3a dumb terminal and modem so I could program from home as a teenager. I got hired f/t at Nike at 19, was making more than my parents combined a couple of years later.