I’m Harry Dry. I left uni, failed with a few startups, finally got traction and left my job to work on Marketing Examples. AMA!
Don't get hung up on the idea of "building a successful startup". Focus on turning yourself into the type of person who builds a successful startup.
I could have launched my first startup 1000 times over and I'd have failed every time. Why? Because other than being able to write some basic html + css I had virtually no attributes of the type of person who makes it.
I could barely code. I was a perfectionist. I'd never heard of Paul Graham. Designing a landing page took me weeks. I had no email list. No connections. No Indie Hackers account. No marketing ideas other than Product Hunt.
Don't get down if your projects aren't working out. Just keep building new stuff, sharpening your talent stack, like Federer at the net, till it turns to muscle memory.