I sometimes wish we could paywall part of 538 but the paywall was you had to demonstrate some knowledge of how probability works.
"4 in 5 doesn't mean 100%" is a *very* important point of emphasis for irregular readers that the regulars maybe don't need to hear as much.
@EricGrenierCBC I'd be interested in seeing an analysis of polling accuracy in North America over the last 10 years. It seems they are becoming less and less predictive.