Because my answer is invariably: build a prototype and see what people think, and that just leads to more questions.
There seems to be a deep resistance to prototyping in marketing culture and I've never really been sure why. We do A/B tests all the time, we make animatics, do sketches and launch trial products, and I guess they're all forms of prototype.
But it's seldom seen as such - and there's almost always a covert air to these things. They're not public and, if they are, then they're not admitted to be experiments. It seems we'd rather let things fail than admit we were just trying something out.
So you'd expect that the biggest and stodgiest entity out there - the Government - would be similarly unfriendly to prototyping, and, for the most part, it has been. Until the other day, and the launch of http://alpha.gov.uk - a website designed first "to test, in public, a prototype of a new, single UK Government website" and second "to design and build a UK Government website using open, agile, multi-disciplinary product-development techniques and technologies, shaped by an obsession with meeting user needs".
It really is a thing of beauty and it's hugely worth examining both the site itself and the behind-the-scenes stories. Go and have a look.
My favourite element is the warning right on top of the front page: "EXPERIMENTAL PROTOTYPE. There may be errors, inconsistencies and inaccuracies." Obviously, that's a necessary alert, but can you imagine telling your clients or management that this will be the first thing people will see when arriving at their shiny new website? That would normally be enough to kill the project right there.
In fact, most of my favourite bits are right up at the top of the page alongside that warning. There's a link to a clear, simple description of the project; there's a link called Tell Us What You Think, leading to a well-thought-out structured section, explicitly designed for discussion and feedback, not a place where comments are grudgingly accepted and seldom replied to.
And, finally, there's a link to the project blog where the site's builders discuss their philosophies, what they've learned and how it's all going. Again, it's clear, well-written and candid, as explicit about issues such as interdepartmental politics as it is about technology decisions. And, on top of all this, the whole project has been a PR triumph - the novelty of the approach and the candour have created all sorts of favourable news and debate. This is how to prototype. Let's have more.