I've been a software developer for ~15 years, but I only started getting really into automated testing the past 6 years or so. It took a lot of iteration, but I finally found an efficient testing strategy which is helping me get releases for my products way quicker than I would otherwise.
My last product was a commercial failure, but people were impressed that I was only spending 20 hrs/week on it instead of 60 hrs/week. Most of those people didn't encounter any bugs either.
I'm working on a new product now and to demonstrate its features (as well as help with onboarding and marketing), I made a guide to automated testing.