Not sure this is a good elaboration - if you know exactly what you want to build, then you're not agile. The point of being agile is that you start off building

Not sure this is a good elaboration - if you know exactly what you want to build, then you're not agile. The point of being agile is that you start off building towards an address book, but along the way you discover that actually what your customers want is something slightly different - so you change the direction you're going in. Agility allows you to follow your customers. If you have a fixed requirements - "we're building a product that does A,B,C and it looks like this" - then you're not agile, and as I point out in the post, agile is NOT a project management methodology. You can use SCRUM, XP, whatever - doesn't make you agile. (And it won't make delivery any faster, just more annoying, as everyone around you will assume it should be faster, and will constantly bang on about why nothing's happening yet.)