You make a good point that I've seen echoed in different ways in different books/articles/talks.

If I can chime in with my take, and I think you had something to this tune in your post, it's important to not only be specific but to be opinionated. You not only have a problem that you've targeted specifically, but you also have the a specific solution.

It reminds me of when I had to write papers in college and the professor would say "Don't just summarize the different sides of the argument, choose one and argue it. I don't care if you're wrong just argue it." I think startups are similar. You pick a side and you come up with a market strategy/argument for it. If you fail, you pivot. But at each step of the way you should have an opinion, an obvious solution that can be conveyed to the user (or investors).