From Evan Williams in a post on evaluating new product ideas:

The key question for evaluating an idea [on the topic of obviousness] is number one: Is it obvious why people should use it? In most cases, obviousness in this regard is inversely proportional to tractability. The cost of Blogger and Twitter’s high tractability was the fact that they were defining a new type of behavior. The number one response to Twitter, still, is Why would anyone do that? Once people try it, they tend to like it. But communicating its benefits is difficult. We’re heartened by the fact that Why would anyone do that? was the default response by the mainstream to blogging for years, as well, and eventually tens of millions of people came around.

Definitely read the rest. But this one spoke to me: while we all understand that for any new product it can be hard to change behaviour, establishing a NEW behaviour is an entirely different beast with a different response mechanism and value proposition. Usually we can fall back on the “is it better, faster, cheaper” viewpoint on evaluating an idea, but sometimes we can hit on idea that captures none of the three because the range of substitute behaviours is so limited.