>Nate Silver just like NYT gave Hillary a 90% chance at the start of the day

He didn't though, and that's my point. What you're saying is factually untrue, they haven't updated their prediction since election morning, and it sits at 71% Clinton [0] (Updated Nov. 8, 2016). If you don't believe that, then you can take a look at archive.is, which provides timestampped copies. This [4] is an archived copy from well before polls closed (3:30 PM), there are others from earlier in the day.

I don't know what led you to believe that it was a sure clinton win, but that just wasn't the case.

Clinton won the popular vote by somewhere between 2 and 3%. National polls from just before the election (also per 538, [1]):

    +4, +2, +3, +4, +4, +4, +4, +4, +2, +3

An arithmetic average of those gives C + 3.4.

Take Florida, a state trump won, here's polls taken in Novemeber [2]:

    +1, -3, +0, +2, +1, -4

An arithmetic mean gives -.5, Trump won by about a percent.

Take Pennsylvania [3], another close state. November polls again

    +1, +2, +4, +6, +3, -2, -2, +0, +0, +2, +2

An arithmetic mean gives Clinton + 1.18, Trump won by about .7, so this was perhaps the greatest polling blunder, and its still a margin of under 2%, which isn't unheard of.

[0]: https://projects.fivethirtyeight.com/2016-election-forecast/ [1]: https://projects.fivethirtyeight.com/2016-election-forecast/... [2]: https://projects.fivethirtyeight.com/2016-election-forecast/... [3]: https://www.nytimes.com/elections/results/pennsylvania [4]: https://archive.fo/4EQGB

I stand corrected, it was 71.4% The 90% from NYT stood out in my mind.