Many martial arts emphasise the importance of using the strength and force of your opponent against them. This is a great teaching which can be developed to a high level and is particularly important in Tai Chi and kung fu, amongst others. But this is not always possible in every situation. This technique involves the use of the opponents own stregnth to complement your own and perform a technique that would otherwise be impossible; however, it actually begins one step before this by manipulateing the opponent into exerting the desired kind of force, thus effectively 'creating' the neccessary force to perform the technique. It is used to overcome 2 opponents simultaneously who are restraining the Ninja.

The situation is this: You have one opponent at either side of you, both of which are holding one of your arms. Unless you are incredibly strong and they are very weak no amount of thrashing and struggling will be able to free you from such a predicament; you just wouldn't have the strength to control both opponents. In this situation you have the additional problem of restricted movements, making it very hard to perform any kind of attack. No significant strike is possible with the arms or head. In fact, only the legs can be used, and they are only able to strike the inside leg of each of your opponents; such a strike would be ineffective on its own.

The only way to take down both opponents is for them to put all their weight onto the inside leg, enabling the NInja to strike to the back of the knee of this supporting leg and take them down. It is highly unlikely that even the strongeest Ninja could pull both men completely onto one leg simultaneously, so the neccessary force must be 'created':

Firstly the Ninja puts both his legs behind the inside legs of his enemies, so the a kneeling motion would pushhis knees into the back of the knees of his opponents, forcing the legs to bend. Then, rather than pulling his opponents inwards onto these legs he does the opposite, pushing them outwards from him with all his strength. The opponents naturally resist this pushing and are now, therefore, pushing inwards towards him themselves. With a swift change of direction the Ninja  is now pulling with the strength of both of his opponents rather than against it, and it takes little strength to pull their weight onto the inside legs, at which point he performs the take-down. The twisting motion of a backwards roll frees the NInja from the grip on his arms.

In this technique the Ninja has literally created the neceessary force from within his opponents themselves, by maniupulating them into doing what he wanted. This is a fairly simple technique which illustrates a very important principle of Ninjutsu.