There is a quote I love from the movie "city slicker" that reminds me of this article

You know what the secret of life is? No, what? This. Your finger? One thing. Just one thing. You stick to that and everything else don't mean shit. That's great, but what's the one thing? That's what you've got to figure out.

And to answer the right question, it is vital to take the users point of view to honestly see if your product will take off.

Imagine how highly motivated you will be when after careful reflection, you know for sure fact that your product will be truly something that everyone will want and that it will be there to last.

"Good products solve a single, focused problem."

We could go semantic and debate product vs. service and all, but I am going to assume that the author means both when he says "product".

What single, focused problem does Second Life solve?

I think the define-and-solve approach is limiting. You stay focused on the status quo. Innovation is a distraction.