The P90X phenomenon has had tremendous influence on how people approach their fitness goals. The advertised driving principle behind P90X is the concept of muscle confusion. The idea that you need to constantly vary your workouts to keep the muscles guessing for maximum fat loss.
This concept is presented by the Team Beachbody people as though they invented the idea. People that have been around for a while know better. The muscle confusion principle was written about the Father of Bodybuilding Joe Weider 50 plus years ago. The difference was that for Joe muscle confusion was considered an advanced bodybuilding training concept. It was not recommended for beginners.
As a pragmatist, if confusing your muscles works for you, be about it. For people not in the advanced bodybuilding stage, some of the smartest minds in fitness advocate a different approach. They recommend that beginners stick with basic fundamental movements.
The reason they advocate this approach is that as simple as many of these movements look there is a whole lot going on in the body. The smart play for beginners is to stick with those movements long enough for the body to learn those movements. By practicing these movements and focusing on the mind-muscle connection you can get better muscle recruitment and therefore better and SAFER progress.
The faulty assumption underpinning the muscle confusion principle in P90X is that you need muscle confusion in order not to be stagnate in your training. The truth is you need a way to progress your training, but there are a million ways to do this other than confusing your muscles.