Keep the main line straight, and you can improvise the details.

The source

"Keep the main line straight, and you can improvise the details." Yamamoto Tsunetomo said it in Hagakure, Book 1. Translated from the original Japanese by Spartan Surfers.

"本筋をさへ立てはづさぬ樣にすれば、枝葉の內、飛手をも、案外の事をも爲して苦しからざるなり"

Original Japanese, Hagakure, Book 1. Japanese: Hagakure, vol. 1 (1937 printing), NDL digital text.

Who said it

Yamamoto Tsunetomo (1659–1719). Samurai turned monk whose spoken reflections were written down as Hagakure, Hidden by Leaves.

Questions

Who said "Keep the main line straight, and you can improvise the details."?

Yamamoto Tsunetomo (1659–1719). Source: Hagakure, Book 1.

What is the original Japanese?

本筋をさへ立てはづさぬ樣にすれば、枝葉の內、飛手をも、案外の事をも爲して苦しからざるなり. Translated from the original Japanese by Spartan Surfers.