Ciro Santilli Mahayana adds a bunch of stuff on top of the Pali Canon. Most of it appears to be random mysticism. Maybe there is something good in it... maybe.
Perhaps the appeal of Zen is that it stepped away from Mahayana's "God and entities", and went a bit back towards the Buddhist psychology-like/self improvement grassroots?
The type of feeling of confusion and distrut for your sense that some Koans attempt to instill.
Ciro Santilli's preferred version of it is physics and the illusion of life.
Some notable references:
- kotobank.jp/word/大疑-556655 quotes passing referenes by
- Nichiren (1272)
What should I do?
- Sasamegoto (1463-64)
The square is without Daigo because there is no doubt
- Nichiren (1272)
- en.wikipedia.org/wiki/Hakuin_Ekaku#Taigi_%E2%80%93_great_doubt mentions Hakuin Ekaku's take
This is perhaps the most popular version of Great doubt in 21st century China
Fuller quote as seen e.g. at: www.hrfjw.com/fjrw/hcrw/ywfs/324750.html
大疑大悟，小疑小悟，不疑不悟translation;
Great doubt, great underestanding. Small doubt, small understanding. No doubt, no understanding.k.sina.cn/article_5668613235_151e02c7300100wutq.html attributes it to modern day Chinese "Master Chongci" (崇慈法师).