Suggested related reading on the topic:
"In Praise of Missing Out: Psychoanalyst Adam Phillips on the Paradoxical Value of Our Unlived Lives"
https://www.brainpickings.org/2015/08/17/missing-out-adam-phillips/
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In the Ask HN link above, a guy says he opened an unread email two years late and saw it was from Facebook in 2009 wanting to hire him.
Similarly, perhaps, one of my regrets was having received an early 2014 email that I didn't open, from someone I didn't much feel the need to keep in contact with. In late 2014, I finally read it. It was an offer to be the personal guide to the US team at the World Cup in Brazil...