We've found a lot of patterns that make things compelling. Next time you watch a movie, set a timer on your watch. At almost exactly ten minutes into the film the exposition and character build up finishes and the plot begins. Why? Because that's been found to be a compelling amount of time to do that. Take more time, and you bore the audience, less and you risk losing them because they don't identify with the characters enough.
But notice I said "most movies". Because it's compelling, it's used often and that makes it unoriginal. Pop songs are all around three minutes and the hook comes at a certain time into the song, every time. So when you make something compelling, you are usually taking away from its originality. If you go for originality, you risk that people won't like it as much.
Genius is when you can make something both unique and compelling. It's rare. And then it's copied to the point where it soon becomes unoriginal. But that moment, when it's beautiful and you've never seen anything like it - that's a wonderful moment.
What Alexander is bringing up is that, while Hollywood films and pop music favors compelling over original, architects usually favor creating something original at the expense of it being compelling. And he is saying that quality without a name is the creation of artifacts that people actually like.
If I remember right, Kent Beck introduced Erich Gamma to Alexander's ideas with the notion of letting users create their experience in software. Erich took it in a different direction obviously, but I can't help but think that Kent had the stronger instinct of what Alexander was trying to say.
We have to remember when creating that startup: It has to be original or everyone will have done it already, but it's additionally about creating something that people will want. And there's the rub. First because that's extraordinarily difficult. But also because the original part is such an extension of your individuality -- it's you -- that then to modify it to adjust it to reflect what to people will like, means taking yourself out of that very personal work.