Lots of people fail to graduate because of a single failing grade in a single class senior year. Or they get suspended/expelled in their last months. Those people certainly didn't miss out on years of education.

Then there are folks like me. I dropped out of kindergarten. I didn't do any structured schooling until I was 16 when I passed a GED and ACT test then went to college for Computer Science and Physics. My GPA in college was 3.89 and I've been a highly competent software engineer for ~20 years. Nothing that I missed from high school has held me back in any significant way.