"One Man In Hillary’s Campaign Warned She Could Lose, And Everybody Ignored Him"

Hubris - "Pride goes before the fall". It's a good short article

In the last days of the campaign, Clinton was the overwhelming favorite according to most experts. Polls showed her with a consistent lead in key states, and several advanced forecasters regarded her chances of victory as 90 percent or more. Even FiveThirtyEight, the most pessimistic major forecaster, said Clinton’s chances were greater than 70 percent.

“Jake Sullivan, Clinton’s policy director—a brainy and nervous former State Department aide who took on an increasingly important political role as the campaign ground on—was the only one in Clinton’s inner circle who kept saying she would likely lose, despite the sanguine polling,” Thrush says, citing Sullivan’s friends. “He was also the only one of the dozen aides who dialed in for Clinton’s daily scheduling call who kept on asking if it wasn’t a good idea for her to spend more time in the Midwestern swing states in the closing days of the campaign.”

But the rest of Clinton’s campaign ignored Sullivan, with his warnings being dismissed so quickly, they weren’t even substantively considered.

“They spent far more time debating whether or not Clinton should visit Texas and Arizona, two states they knew she had little chance of winning, in order to get good press,” Thrush says. Just a week before Election Day, Clinton made a campaign stop in Tempe, Arizona.

The end result was that Clinton’s campaign went into the final days utterly convinced the race was in the bag and Trump had no shot.

I've read elsewhere that Bil Clinton also wanted the campaign to spend more time in the Midwest but was ignored.