A law of the Universe, that states that there is a finite amount of ninjutsu available to each side during any given battle. If there are many ninjas, they are all awarded a fraction of the total ninjutsu, or 1/N where N is the number of ninjas present in the fight.
This is the reason why hordes of ninja warriors will be dispatched relatively easily, whereas the lone ninja is almost unstoppable.
Practical applications of the law of Conservation of ninjutsu:
Sir! There's an army of ninjas heading this way!
Don't worry, we can take them.
Oh wait... it seems they've given up, sir. There's only one guy.
Ninjutsu is the ancient art of the ninjas (Aka shinobi) of Japan. It is a unique method of moving and thinking which developed our system often referred to us the art of winning. Taijustu is the basic defence method used. This method of relaxed continues body movement allows the user to create a never ending supply of effective counters to any given defence situation and is unique to Ninjutsu. Ninjutsu is a complete fighting system dealing with the Physical, mental and spiritual aspects of student development. Techniques cover locks, throws, ground fighting, multiple attacks, modern weaponry, and all types of traditional Ninjutsu weaponry. In fact in Ninjutsu, there is no restriction on the type of available technique we can add on to our taijutsu. The power of this relaxed system has to be experienced to be appreciated.
Ninjutsu did not come into being a specific, well-defined art in the first place, and many centuries passed before Ninjutsu was established as an independent system of knowledge in its own right. The Ninja, at the beginning did not use that label for themselves, they were merely practitioners of strategies that were cultural opposites of the conventional outlooks of the ruling Japanese Samurai class. Their highly illegal counter culture went underground and it was for this reason alone that the art was shrouded by centuries of mystery and deliberate confusion in Japanese history.
Retarded kids whom consider themselves intelligent because of their Counter Blox inventory. You can usually find them lurking in the Ninja's Trade server on discord, prowling the text channels in search of unsuspecting prey to shark. They tend to be vile and vocal creatures, with their one liners being, "WhAt AbOuT dEmAnD" and "CaStLeRs AnD aImEr AbUsE tOo MuCh".