He has a little book called "Zero Mass Design", the premise of which is that if you're going to work on something - for instance, you're going to write a book, or you want to write some software, or you are about to embark on any project that requires planning -- start with a simple design. But it's more extreme than just keeping it simple; you start with a design so simple that it won't work. That requires a great deal of discipline because you go into the project with the premise that you will fail; until you've tried something and actually seen it fail, yoiu don't know how simple you can get.
Does it sound familiar? Sounds sort of agile doesn't it? The explanation that he gives next is the best I've read for "Do The Simplest Thing Possible" mantra of XP. Read on:
Dave Thornburg's example, from James Adams' book "Conceptual Blockbusting", is the Mariner IV spacecraft. It had large solar-cell panels that unfolded. The problem, as stated, was to have a mechanism that slowed down the panels as they unfolded so that they wouldn't break when deployed. So, they tried oil, but that was sort of messy, and they tried springs; they did all sorts of things. The day for the launch was coming nearer and nearer. What were they going to do? Remember, the problem as stated was to find a way to slow down the panels, or to find a braking mechanism. Finally, somebody had the brilliant idea to try it with nothing, so they tried it and the panels shook and shivered but nothing broke. If you state the problem with assumptions, you're going to get them. You're got to pare back and pare back and pare back. Starting with a very simple design has wonderful advantages, but it requires a pyschological twist; you have to expect that it will fail and enjoy that.
I like to get requirements stated in goals which is a trick I learned from use cases. Get the problem stated as a goal and a lot of assumptions can be removed. You'd be surprised how well it helps. The point is not only to "Do The Simplest Possible Thing That Will Work", but state the problem as "Simply As Possible". It removes assumptions and thus, doesn't color your design with needless complexity. Those words slapped me in the face and it seemed everything came together. Wow.