During the years of high economic growth and rising real estate prices the main bank system had its own underlying rationality. Indeed, Japan could not have achieved high economic growth under the system if it had not been rational. However, the system has gradually become incompatible with the changing economic environment.
This change was already evident even before the emergence of the asset price bubble, and it has been further confirmed since the bubble's collapse. Yet, there does not yet appear to be a consensus explanation of the reasons behind the malfunctioning of the system.