The Nikkei average has deviated sharply from the textbook model of stock averages which grow at a steady exponential rate. The average hit its all-time high on December 29, 1989, during the peak of the Japanese asset price bubble, when it reached an intra-day high of 38,957.44 before closing at 38,915.87 https://en.m.wikipedia.org/wiki/Nikkei_225Peak 38,916 (1989)
Bottom 8,160 (2011)
Now 20,080 (2017)
A lot can happen over 25-30 year time spans. (Do you still want to catch a falling knife?) If you own an international equity index fund (as I do) which tracks the
FTSE- Ex-North America Developed Markets Index, about 23% of that is invested in Japan. Of course, there are other markets/indexes in Japan as there are in the U.S.