Ask HN: Does becoming a successful startup depend on having maintainable code?

Yes, it does. Bad architectural and engineering practices will start to burn you at a couple thousand lines of code. "Maintainability" isn't some far-off property that begins to matter when you're at hundreds of thousands of lines.

For the record, the best way to learn software architecture (what works, what doesn't) is to maintain your own code. Only when you support a project from inception to maturity do you get a sense of how much architecture matters and why it is so important.