Who said "Courage is like a muscle. We strengthen it by use."?

This quote is attributed to Robert Frost.

Courage is like a muscle. We strengthen it by use. - Robert Frost

"Courage is like a muscle. We strengthen it by use."

Robert Frost Courage

Poet American 1874–1963

"Two roads diverged in a wood, and I took the one less traveled by."

"The only way out is through."

"Good fences make good neighbors."

"Fire and Ice."

"Never let fear stop you from chasing your dreams."

"Courage is being afraid but doing it anyway."

"Sometimes you gotta do what you gotta do."

"Sometimes you have to be the monster to stop the monsters."