Growing up no one in my family had a professional job. Most of them didn't even work. So while I knew that in theory I could get a CS degree and have a software career, it wasn't something I really felt in my bones. Even after I got the degree I did not feel confident that one of "us" could get a job like one of "them", especially when you're raised with that working class crab mentality.
Later on, it was getting my first self employed contract. I had dreamed about going solo, but always doubted I could pull off. Then it was getting my invoice paid by a director of an overseas company I had never met. Something I knew was possible but felt like utopian science fiction when I read it on HN.
So as cheesy as it sounds - my career has changed my life forever. The realisation that I didn't have to struggle to make ends meet, and that I was in the drivers seat of my own life.