While I am not an expert, the most common cited cause for the Japanese stagnation is the late '80s Japanese asset bubble, possibly worsened by the '85 Plaza Accords where US significantly devalued its currency USD, via currency market manipulation.
From a wider perspective, individuals and countries alike are subject to economic forces that sometimes are beyond their control. The American cultural habit of attributing, without rest, ill fate to moral failing, lacks in nuance. Possibly a byproduct of the historically unique wealth of opportunity bestowed onto the post-war generation.
https://en.wikipedia.org/wiki/Lost_Decades