Sometimes your best friends can inadvertently become your worst enemies. Such was the case of Hillary Clinton and the mainstream media according to Nate Silver of FiveThirtyEight. Most observant people knew that the MSM was all in for Hillary this past election to the extent of acting like cheerleaders for her. So instead of cautioning Hillary when Donald Trump made exactly the right moves to win the necessary electoral votes for victory, they instead mocked him for his ignorance of political campaigning. As a result this gave the Hillary campaign a false sense of security when they should have campaigned more extensively in the previous "blue wall" states of Wisconsin, Michigan, and Pennsylvania.

Silver explains in great detail how the MSM helped lead Hillary to her shocking election loss:

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...Trump was pretty close to having an optimal Electoral College strategy as judged by our tipping-point calculation. Clinton made a couple of mistakes, meanwhile. So did campaign reporters, who usually lauded Clinton’s strategy while maligning Trump’s, making essentially the same errors that the Clinton campaign did. ...Like any other kind of organization, campaigns are subject to internal politics and potentially misaligned incentives, and their decisions can be influenced by outside groups, such as donors and the media. Making the technically correct decision may not be easy if it contradicts the conventional wisdom,7 and correct Electoral College strategy (i.e., not necessarily campaigning in the closest states if they aren’t near the tipping point) is often slightly counterintuitive. Speaking of the conventional wisdom, we should talk some about how the media covered Clinton’s and Trump’s Electoral College tactics. Being among the most technical aspects of the campaign, this was generally not a strength of mainstream coverage. For instance, on Oct. 30, The New York Times jabbed at Trump for “campaigning well outside the traditional band of states that decide presidential elections,” including in New Mexico and Michigan, “two solidly blue states where polling has shown Mrs. Clinton with a clear lead” — failing to recognize that they were potentially tipping-point states even if Clinton was ahead there. A few days later, on Nov. 3, the Times criticized Trump for campaigning in too wide a range of states...

Here is an excerpt provided by Silver of the Times' mockery of Trump's campaign:

Rather than wielding data and turnout machinery as tools, Mr. Trump has instead battered at the political map in a less discriminating way, trying to shift the national race a point or two in his favor and perhaps find a soft spot in Mrs. Clinton’s support.

In contrast to the Times, Silver highly praised this tactic:

This was, it would turn out, pretty much exactly the strategy that swung the Electoral College to Trump.

Therefore a big factor in Hillary's loss was the MSM leading her campaign astray with poor reporting:

To some extent, the media’s misconceptions about Electoral College strategy and Clinton’s errors may have reinforced one another. ...the media tended to read these tactical decisions as revealing a candidate’s absolute strength, rather than the relative importance of the states. A foray into traditionally Republican Arizona, for instance, would be read as a sign of strength for Clinton while a trip to traditionally blue Wisconsin would be seen as an admission of weakness. If a candidate was too concerned about her media clippings, that could inhibit correct decision-making. One wonders whether the reason Clinton never totally abandoned Iowa, for instance — even though she rarely polled well there and it was highly unlikely to be the tipping-point state — is because doing so would have occasioned a media freakout. Conversely, Trump’s data team wasn’t likely to get a lot of credit from the media almost no matter what it did. With rare exception, reporters tended to portray Trump’s Electoral College strategy as being whimsical and haphazard, even when it was doing some pretty smart things. That may have helped Trump’s team to shut out the noise and maximize its candidate’s chances of winning the election.

p.s. Notice that in his entire article the word "hackers" as in "Russian hackers" appears not at all. What Silver emphasized was that if Team Hillary not been led astray by the overconfidence and poor reporting of their MSM allies, the election could have had a different outcome. So in the end her MSM friends had a much greater bad effect upon Hillary's campaign than any imagined Russian hacking.