“The battle had been invisible to the naked eye, but the hardest ones are.”
Source: Shadowfever
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Karen Marie Moning 304
author 1964Related quotes

“The hardest battle you’re ever going to fight is the battle to be just you.”
Speaking Of Love (1980)
Variant: The hardest battle you are ever going to have to fight is the battle to be just you.

As quoted in Blackthink: My Life as Black Man and White Man https://en.wikiquote.org/wiki/Special:BookSources/0688011632 (1970)
1970s

“It is only with the heart that one can see rightly, what is essential is invisible to the eye.”

infinity plus interview (2001)
Variant: In real life, the hardest aspect of the battle between good and evil is determining which is which.
Context: The battle between good and evil is a legitimate theme for a Fantasy (or for any work of fiction, for that matter), but in real life that battle is fought chiefly in the individual human heart. Too many contemporary Fantasies take the easy way out by externalizing the struggle, so the heroic protagonists need only smite the evil minions of the dark power to win the day. And you can tell the evil minions, because they're inevitably ugly and they all wear black.
I wanted to stand much of that on its head.
In real life, the hardest aspect of the battle between good and evil is determining which is which.

“It must be visible or invisible,
Invisible or visible or both:
A seeing and unseeing in the eye.”
Notes Toward a Supreme Fiction (1942), It Must Be Abstract
Context: p>It must be visible or invisible,
Invisible or visible or both:
A seeing and unseeing in the eye.The weather and the giant of the weather,
Say the weather, the mere weather, the mere air:
An abstraction blooded, as a man by thought.</p

“The deaf eye sees what is invisible to the hearing eye.”
Source: As quoted in https://twitter.com/emilioinsolera/status/725116275349950465(April 26, 2016)

“Sometimes the heart sees what is invisible to the eyes”