“If there is any possible consolation in the tragedy of losing someone we love very much, it's the necessary hope that perhaps it was for the best.”

Gilbert Keith Chesterton, as per Mackay's The Harvest of a Quiet Eye, A Selection of Scientific Quotations (1977), p. 34.
Misattributed

As quoted in Mackay's The Harvest of a Quiet Eye, A Selection of Scientific Quotations (1977), p. 34

Adrienne Willis, Chapter 14, p. 152
2000s, Nights in Rodanthe (2002)

Source: House of Leaves

Source: The Museum of Innocence

"Let It Die"
Let It Die (2004)

Disputed
Source: Claimed to be from Men Without Women, but it does not appear in that work. May have originated in a 2011 blogpost by Marc Chernoff entitled 30 things to stop doing to yourself http://www.marcandangel.com/2011/12/11/30-things-to-stop-doing-to-yourself/.