https://fivethirtyeight.com/features/fi ... -forecast/
This is the site from guy that told the media that Clinton wasn't a sure victory (he gave Trump around 28% shot). Part of the first article addresses how odds work - namely that even with a 99.9% chance, that doesn't mean it's impossible to hit that 1 in 1000 shot. The second article talks about their final poll models and gives different scenarios - like if the polling error is the same from 2016 (both towards Trump and towards Biden) - and other caveats like how early voting makes later polling difficult.
I don't see mass protests at a Trump win - I see mass protests at a Trump win if the courts intervene and do something like make the cutoff date today for votes to be counted. Votes have never been finished counting on election day in modern history.
From the second link above:
This includes me. I swore off the two big parties in 2009. Now I'm a hypocrite because I felt I had to vote Biden this year (I'm probably a hypocrite other ways too, just now including this one). Ranked choice can't come soon enough.The lion’s share of people who voted for Gary Johnson or another third party candidate four years ago also say they plan to vote for Biden.