Well...

If you don't know what you're trying to build, you probably aren't going to manage to build it. But in practice, you never actually know for sure, because things always change.

You should know how you're going to build it (the architecture). But in practice, my ability to be omniscient is very limited. As I implement it, I find out that my design/architecture was wrong.

Maybe the key factor is this: When you find out that the architecture is wrong, do you fix it? Or do you just hack it to get the next bit to work?