> Most people do not spend thousands of hours building something "not knowing what they're building."

They sure do in my experience.

> On the contrary, in my experience it's much more important to "play" with a concept and see it working...

I agree with all that. That's the point: figure out what you're trying to do before building it. Of course you will not know everything up-front, and of course you would try things out to learn and progress, and, for anything that it's tiny, of course it makes sense to do this iteratively, working from the most pressing/important/risky points earlier.

Or, at least, it seems obvious to me.