The solution
In September 1982 a physics thread on Carnegie Mellon's bulletin board posed a free-falling elevator puzzle involving a candle and a drop of mercury. Howard Gayle replied with a fake warning that an elevator had been contaminated with mercury and fire-damaged. Some readers took it seriously, and the group began discussing how to mark non-serious posts.
Neil Swartz proposed putting a star in the subject line of jokes. Others suggested %, & and {#}, and one group on the Gandalf VAX had used a smile symbol. Two days after Swartz, Scott Fahlman posted: 'I propose that the following character sequence for joke markers: :-) Read it sideways.' He added :-( for things that are not jokes.
Terminals showed only the 95 printable US-ASCII characters, so a punctuation-based face worked on any of them. Ars Technica stresses the idea was collective: Fahlman combined single-character simplicity, a face-like look, the sideways reading hinted at by {#}, and both states.
What it achieved
On ASCII-only terminals, build a face from punctuation that reads sideways, with one symbol for jokes and its opposite for serious posts.
Why it worked
Text lacks the body language and tone of voice that signal a joke.
A face made from standard punctuation needed no new hardware.
A joke marker plus a serious marker covered both cases.
It was small and memorable, so it spread by copying.
What can be applied
Adoption goes to the proposal that merges the best parts of earlier ideas within the tools everyone already has.
Aftermath
Per Ars Technica, the emoticons spread across ARPAnet to other universities and labs, and by 10 November 1982 James Morris was introducing them to colleagues at Xerox PARC. The original thread was thought lost until a 2001-2002 effort recovered it from 1982 backup tapes. Fahlman himself says he may not be the first ever to type those characters.
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