Just as much as our job is to build something genuinely useful, something which really does make people’s working lives simpler, more pleasant and more productive, our job is also to understand what people think they want and then translate the value of Slack into their terms.
However, almost all of them have no idea that they want Slack. How could they? They’ve never heard of it. And only a vanishingly small number will have imagined it on their own. They think they want something different (if they think they want anything at all). They definitely are not looking for Slack. (But then no-one was looking for Post-it notes or GUIs either.)