It always ends.

"It always ends. That's what gives it value." - Death

Context: Death manifests itself as a teenage girl to live amongst humanity to remember the value of life. At the end of the manifestation she merges back with her celestial self after discussing her experience.

Lesson: We only appreciate life because we know that it ends. It's the struggle to keep living that makes it worthwhile.

References: Taken from Death: the high cost of living TPB (ISBN 1-56389-133-6) by Neil Gaiman (writer), Chris Bachalo (artist), Mark Buckingham (artist) and Dave McKean (artist). Published by Vertigo, an imprint of DC Comics.