Who said "Keep your mind wide and straight. Not tight, not slack."?

Miyamoto Musashi (c. 1584–1645). Source: The Book of Five Rings, Water (The Mind in Strategy).

What is the original Japanese?

心を廣く直にして、きつくひつはらず、少もたるまず. Translated from the original Japanese by Spartan Surfers.

Keep your mind wide and straight. Not tight, not slack.

Miyamoto Musashi, The Book of Five Rings, Water (The Mind in Strategy)

The source

"Keep your mind wide and straight. Not tight, not slack." Miyamoto Musashi said it in The Book of Five Rings, Water (The Mind in Strategy). Translated from the original Japanese by Spartan Surfers.

"心を廣く直にして、きつくひつはらず、少もたるまず"

Original Japanese, The Book of Five Rings, Water (The Mind in Strategy). Japanese: Miyamoto Musashi (Kinkodo, 1909), NDL digital text.

Who said it

Miyamoto Musashi (c. 1584–1645). Undefeated swordsman who wrote The Book of Five Rings in a cave a few weeks before he died.

Questions

Who said "Keep your mind wide and straight. Not tight, not slack."?: Miyamoto Musashi (c. 1584–1645). Source: The Book of Five Rings, Water (The Mind in Strategy).
What is the original Japanese?: 心を廣く直にして、きつくひつはらず、少もたるまず. Translated from the original Japanese by Spartan Surfers.