Jim Matthews
Japanese planes aren't just flat.
They have two (or three) contact points that must be in a plane with the exposed blade.

This requires removing the equivalent thickness of fine rice paper between the contact points.

Japan is almost entirely coastal and subject to Seasonal humidity changes. While air conditioning might help reduce the moisture content in the wood body, heating season will cause the opposite problem.

These Seasonal differences are exaggerated by the adjustment of the sole. It's *a lot* of fuss, but worthwhile in some applications.

I suppose the greater cross section of Western style planes resists twist and cupping, to some degree, but that's above my pay grade.

https://brianholcombewoodworker.com/2016/08/11/kanna-dai-prep/