[miguelos]

Let me disagree.

Unless you plan to discover new ideas by mistake, you absolutely need a vision, and then find the way to get there.

If you start from the bottom (bottom-up), you'll constantly compromise technically, as lots of things are not yet possible to do.

If you start from the top (top-down), you'll "know" that it's possible to accomplish, and you'll only have to find out how to do it.

You have far more chance to solve an enigma if you know there is an answer than if you don't. Visionary ideas make you believe the answer exists, which makes it much more easier to accomplish.

[ajju]

Let us say your goal is building a search engine.

Clearly, you have to "know" that it's possible to accomplish and then find out how to do it. I don't think even PG was disagreeing with that.

When he says "don't have a blueprint", he is saying don't presuppose you know how to get from where you are to replacing Google as the de facto search tool. Instead, just make progress. It seems you agree with that.