[Zigurd]

This is all correct, and following this advice will improve your project planning. BUT it skirts the problem that Agile makes people think they can plan a project without knowing what's a functional spec, what's an implementation plan, and what of those things is implied by a user's desires. You can't arrive at a really good plan just writing more-concise stories that don't span too many hidden requirements. It helps, but it isn't a substitute for domain knowledge and systems analysis training.

[UK-AL]

The hard part for agile projects is that you only loosely know what is the desired end result.

Specs should and will change.

[Zigurd]

That's the good part about agile. The bad part is that the idea of a "story" goes a bit too far in trying to make specification creation accessible. Decomposing stories into smaller pieces is a solution that's palatable to many because it avoids the hard work: Gaining more domain knowledge, and developing critical thinking.