This does only work if the system guarantees that you'll reach whatever you set out to do. I don't think that is the case most of the time. Even in his example:

> In the last 12 months, I've written over 115,000 words. The typical book is about 50,000 to 60,000 words, so I have basically written two books this year.

No, he hasn't written two books. A book is usually not a collection of random articles, but has a clear structure. Furthermore, only writing the book will never get it published. Whether one wants to self-publish or work with a publisher, both things will need a significant time/work investment at various points in time, and will most likely not be covered in his (initial) system.

Similarly, if you wanted to launch a software business, you'd probably create a system that includes writing software. If you're good, it may also include talking to users. If you'd forget about your goal and just followed that system, you'd never launch. Even if you arrive at a state where you want to release your software, you need to (consciously) break your system and care about one-off tasks like setting up a company, terms of service and what-not.