This long post by Jesse Singal makes one key point perfectly clear: People on Twitter may know that 10,000 alarmist posts about their political enemies have been thoroughly debunked and discredited, but when that ten-thousand-and-first comes along they’ll instantly retweet it and add, “CAN YOU BELIEVE THIS CRAP???” And of course the lies will get a hundred times the exposure of the corrections. We all do well to remember Mark Twain’s “Advice to Youth”:

Think what tedious years of study, thought, practice, experience, went to the equipment of that peerless old master who was able to impose upon the whole world the lofty and sounding maxim that “Truth is mighty and will prevail” — the most majestic compound fracture of fact which any of woman born has yet achieved. For the history of our race, and each individual's experience, are sown thick with evidences that a truth is not hard to kill, and that a lie well told is immortal. There in Boston is a monument to the man who discovered anesthesia; many people are aware, in these latter days, that that man didn't discover it at all, but stole the discovery from another man. Is this truth mighty, and will it prevail? Ah, no, my hearers, the monument is made of hardy material, but the lie it tells will outlast it a million years. An awkward, feeble, leaky lie is a thing which you ought to make it your unceasing study to avoid; such a lie as that has no more real permanence than an average truth. Why, you might as well tell the truth at once and be done with it. A feeble, stupid, preposterous lie will not live two years — except it be a slander upon somebody. It is indestructible, then, of course, but that is no merit of yours.