“I want to see the king.
Wonderful. I'm glad for you.
Why are you so glad?
Because it's good for every human being to have an unfulfilled wish. It makes all of life so poignant.”

http://www.people.com/people/archive/article/0,,20095610,00.html

Source: Soldiers Live (2000), Chapter 99, “By the Military Cemetery: Missing Persons” (p. 664)
Context: “It doesn’t make much sense, does it?” my darling whispered to me. “People go at the oddest times and from the oddest causes.”
“Soldiers live,” I muttered.
“You’re turning that into a mantra.”
“You feel guilty. You wonder why him and not me, then you’re glad it was him and not you, then you feel guilty. Soldiers live. And wonder why.”

Canyon, Texas, (September, 1916), p. 187
1910s, Letters to Anita Pollitzer' (1916)

Variant: Why think about that when all the golden land's ahead of you and all kinds of unforeseen events wait lurking to surprise you and make you glad you're alive to see?
Source: On the Road

Source: Hogfather

John Banville: Who cares whodunnit? (2013)

How to Raise a Prodigy, The New Yorker (2018)

Source: City of Fallen Angels

Ah, poder ser tu, sendo eu!
Ter a tua alegre inconsciência,
E a consciência disso!
"Ela canta, pobre ceifeira" ["She sings, poor reaper"], first published in Athena, no. 3 (December 1924); trans. Richard Zenith, A Little Larger Than the Entire Universe (Penguin, 2006)