To me, the "do what works for you" that I say quite often doesn't mean "Do anything, and you'll be guaranteed to be healthy and reach your goals". I just mean that for some people, one method like Primal doesn't resonate in a way that makes it effortless (one of the key words on the front of the PB book!) so they STRUGGLE. If it's a struggle, they won't stick with it anyway.
As the extreme example, think of our resident Shrinking Violet. Primal is a daily-hourly-minute-by-minute struggle in misery for her. It's not because primal doesn't work, it's because primal is not the right solution at this point in her life for the problems that she individually is facing.
Also, no way-of-life is guaranteed to give you abundant health for 100 years. People manage to live a life of very poor health habits, and live long. Others live as perfectly as possible, and die young. That's why it's not worth struggling beyond reason or suffering beyond reason if a particular plan--including primal--isn't working for you.
Zone diet on and off for several years....worked, but too much focus on exact meal composition
Primal since July 2010...skinniest I've ever been and the least stressed about food