“Don't fear death, fear the un-lived life”
Variant: dont be afraid of death, be afraid of the unlived life.
Source: Tuck Everlasting
Help us to complete the source, original and additional information
Natalie Babbitt 14
American children's writer and illustrator 1932–2016Related quotes
Variant: Don't be afraid of death; be afraid of an unlived life. You don't have to live forever, you just have to live.
Source: Tuck Everlasting: Scholastic Book Guides

Not by Twain, but from Edward Abbey's A Voice Crying In The Wilderness (1989).
Misattributed

“People who fear death live no longer than those who don't, and live scared.”
The Wizard Knight (2004), Volume 1: The Knight, Ch. 62
Fiction

“Until we know that death is equal to life, we live in fear.”
Loving What Is: Four Questions That Can Change Your Life (2002)

“Less base the fear of death than fear of life.”
Source: Night-Thoughts (1742–1745), Night V, Line 441.
“It is not death that a man should fear, but he should fear never beginning to live.”
Marcus Aurelius, p. 225
They Both Die at the End (2017)