I like this post and find some of it quite helpful as a framework, but certain pieces are sufficiently vague that I actually have no idea what's being said:

"As a rule with few exceptions, you want to move forward through iteration loops, not backward. (Too often, moving backward is a sign of problems with doing, not problems with planning.)"

What does that mean? a short example here would help. How do I know if reprioritizing is going backwards or a problem of doing vs. what was advised up above?