In reading history he also said that they were afraid they’ve awaken a sleeping giant. How true were those words. Karma really works since the torpedo’s used at Pearl Harbor were made in Nagasaki.
That quote came from a movie. There is no evidence that he ever said that in reality.
The actual quote where he predicted the future is verified: “I can run wild for six months … after that, I have no expectation of success.”
More here: https://en.wikipedia.org/wiki/Isoroku_Yamamoto%27s_sleeping_giant_quote
Yamamoto is one of those guys that these days an intelligent government agent would have decided to try to extract along with his family before hostilities started. A good, loyal and capable officer sadly fighting for the wrong side.