The short and sweet is coaching. Can CrossFit be done without a coach? Sure, but it won't be as effective, efficient, or as rewarding in the long run. Certainly, most people who come to CrossFit have trained on their own for years and have reached a point where they've plateaued - mentally or physically, or both. Training in a CrossFit gym (or box as we like to call ...it) can be humbling, eye-opening, and make fitness "fun" again for those who've lost interest in fitness over the years. Humbling because one realizes they're not as good as they think they are.