For me, it was finding out you could add custom templates to your MySpace page by copy/pasting blocks of code into sections of your profile. If you remember, you could make your background look like a matrix screen and your cursor look like it was on fire. The templates I found didn't quite look the way I wanted them to look, so I started combing through the html and tweaking numbers around until it looked the way I liked.
I thought it was fun, so I signed up for a web design class in high school. Everything on the curriculum I had already learned from decking out my MySpace profile, so I started learning flash animation using ActionScript during class time.
Flash forward, I'm now a front-end developer and it's all thanks to MySpace 👍