Fujibayashi Yasutake

"Secret techniques to infiltrate without fail are deceptive ways which are varied and flexible and are done according to opportunity. Thus, as a basis, you should embrace the old ways of the shinobi who served under ancient great generals, but remember not only to keep these ways but to adapt them, each dependent on the situation and the moment. Ignorant ninja are not aware of this principal but directly stick to ancient ways and do not even know the simplest of facts..."

"It is folly to see something as unchangeable and stick to an old method without realizing that things keep changing and are in flux."

Fujibayashi Yasutake, 1676. Bansenshukai