Worse than just believing it … these days they can (nearly) instantaneously share it to zillions of other people around the world many of whom will also believe (and re-share) it, and few in that chain will bother to fact-check it themselves, and of those few, even fewer will take the time to call out the error / misinformation, and even if they do, they'll almost instantly be shouted down and ridiculed by all those who just outright refuse to see facts when they really really want to believe a lie. This of course leads the average "volunteer" fact-checker to just sooner or later give up even trying to fight the growing waves of "fake news", and keep their fact-checking to themselves; Not good for anyone.
Actually it seems that quote may have originated from Johnathan Swift not Mark Twain, although almost everyone attributes it to Mark Twain. Which is rather nicely recursive given the subject of the quote.
The quote doesn't look like Swift's style of English; so I read that buzzkill article. What buzzkill attributes to Swift isn't the quote (or its origins), but the sentiment. Swift has nothing to say about how long it takes to put on shoes.
There are actually quite a few quotes attributed to Twain (and Einstein, and Lincoln, and many famous "others") that may or may not have been said first (or at all) by the people they're attributed to. Interesting "rabbit hole" to explore for those into that sort of thing…
