The best ideas in life are simple: When you first come into Jiu Jitsu it is natural to get a little overwhelmed at the seemingly endless number of moves and variations of those moves. It can seem an impossible task to learn them all and become even proficient in them, forget about master them. Always remember that the underlying PRINCIPLES and concepts of Jiu Jitsu are much much fewer in number and very simple to understand. Jiu Jitsu is divided between a TOP GAME (when we play on top of our opponent) and a bottom game (when we play underneath an opponent). When it comes time to play bottom game the central directive of Jiu Jitsu is very simple – ALWAYS SEEK TO KEEP YOUR LEGS/HIPS BETWEEN YOU AND YOUR OPPONENT TO MAXIMIZE YOUR OFFENSIVE AND DEFENSIVE POTENTIAL – IF YOUR OPPONENT GETS PAST YOUR LEGS, RECOVER LEG POSITION FIRST BEFORE YOU ATTEMPT ANYTHING ELSE. That is the whole bottom game of Jiu Jitsu in a nutshell. All the myriad techniques and tactics you will learn over the years in bottom position are just an expression of that statement. The reason for this is also simple. It is based upon a fundamental truth of the human body. HUMANS ARE MASSIVELY STRONGER IN THE LEGS/HIPS THAN THEY ARE IN THE UPPER BODY. This fundamental strength/endurance asymmetry between our upper and lower body provides the SINGLE GREATEST HOPE FOR SMALLER/ WEAKER PEOPLE TO DEFEAT BIGGER/STRONGER OPPONENTS IN UNARMED SINGLE COMBAT. If you can wrestle with your legs against a bigger persons upper body the inherent upper body/lower body asymmetry can be used to advantage as your legs/hips will be stronger and possess more endurance than his upper body. That is why your two first skills in Jiu Jitsu must always be the ability to recover your legs back between your opponent (ie to escape a pin) and the ability to prevent someone ever getting past your legs in the first place (guard retention). Those two skills are the basis of the bottom position in Jiu Jitsu – everything else presupposes them.
