The likely failure of a start-up is market based, not technology. Look at Twitter's fail-whale years. They were on a platform which couldn't scale to their growth and it took many months for them to re-architect and build a working solution. It definitely didn't kill them.

Another example is Instagram, I read recently (but can't find the link) that the founders were learning to code when they built it, and that some of that code is still in production, and apparently, it's embarassingly bad, but it gets the job done.

On the other hand, I worked for a consulting firm and one of our clients sites was absolutely riddled with technical debt. The result was that any changes they wanted to make were significantly more expensive than if they would have been on a better architected system. The thing is, it did't matter to them because the cost of re-creating the system was significantly more than the cost of working with what they had.

I hate technical debt, but have come to realise that it is a debt much like any other, and if you can cover the cost of that debt, it doesn't really matter down the line.

This isn't an excuse for bad programming, I consider that to be something slightly different from technical debt which often works but is not an idea implementation.