Love of Power
Perhaps the greatest challenge to human civilization is how its leaders are chosen. We want selfless and honest people at the helm, whose ambitions lie no further than the well-being of the common man.
Yet there is no mechanism by which this can be made to happen, since the love of power is generally what motivates people to aspire to the top positions in government.
Worse, as educational standards fall, we get what happened in 2016 here in the United States, where we elected a sociopath to the White House. And here we find ourselves, seven years later, with Donald Trump still supported by tens of millions of voters.