He defines insight in terms of its effect rather than its inherent qualities. An insight is creatively generative, it leads people to think in a new way about something, to see a whole new field of effective possibilities that had been invisible. And in order to be evocative in this way, it has to be kind of allusive. It must "avoid the direct and the explicit".
This last part is what makes the article truly (and recursively) insightful for me. An insight has to be interesting. It can't just be a statement of fact that is then made interesting through creative interpretation. It has to be based in fact, but have gaps to be filled in, that beg to be filled in, by the reader.
I used to think that we had to come up with a catchy summary of each brief so that the client and agency would have a quick and attractive "elevator shorthand" to communicate and sell the idea internally. Over the past few years, I've come to see that the elevator phrase, truncated, alliterated and, strictly speaking, inaccurate though it may be, is usually a better, more insightful, brief.