I never worked in tech. I started learning programming at a young age with BASIC, thinking I know everything, gotos are good, single letter variables are good etc. Even arguing with teachers when my working but spaghetti code got marked a low grade. Probably the reason why I didn’t end up in tech.
My background is similar to GP's. I would say that my first inkling that something was wrong was working alongside someone more egregious than me. I also spent half of my career supporting a product built by someone who sold his company to my employer, started another company writing add-ons for the product he'd just sold and sold that to my employer, then started another project and sold that to Google. Six years of cleaning up his messes was enough.
I really don't know of a way to learn that lesson other than the Hard Way. I definitely remember coworkers pushing back on my ideas and writing them off as boring and unambitious. Fortunately they had seniority over me, so most of my harebrained schemes never saw the light of day.