Disclaimer: not mine. I just play in Kripke's toychest. Tag to S8 "Trial and Error"

"It was starting to end, after what seemed most of eternity to me." Sam wondered what had compelled Zelazny to write those words, but they were never more an apt description of what he felt, as the light in his right arm slowly faded. He decided, then, that he would keep the truth from Dean; protect Dean from his own self-sabotaging big-brother instincts. He knew, of course, that Dean would find out eventually, but he wanted to let his brother believe, just for a little longer, that the light at the end of the tunnel would illuminate both of them.

Quote is from Roger Zelazny's Nine Princes in Amber, opening line chapter 1.