1.Why are people SOOOO sure that we won't know the results of the election for quite a while? From what I remember, in 2016, we knew it on the same day!
A ton of people are voting by mail
While historically mail voting hasn't been that biased towards either party, this year we know it will be extremely biased towards Democrats because Trump has been politicizing VBM
Some states (including, in particular, Pennsylvania) don't allow election officials to begin counting mail votes until election day
In some states mail ballots can arrive several days after election day as long as they were postmarked by election day
States will be inconsistent about the order in which they report the votes, so we can expect some states to swing from large Trump leads to Biden leads (or vice versa) as they count ballots from different modes