Just look at how people who are otherwise sane and courteous（adj.办有礼貌的;谦恭的）behave online：the arguments, the sarcasm（n.讽刺;挖苦）, the aggression, the abuse. Of course human beings have always been capable of fighting, but something strange happens on social media. For one thing, confrontation on the screen happens more often than it ever would in our daily lives. Put a device in people's hands，and suddenly they're on a hair-trigger—either（hair-trigger adj.一触即发的）giving or taking offence.

One crucial（adj.重要的;决定性的）factor is social media's ability to stage a confrontation（n.对抗;对峙）in public. Suddenly two individuals will be slugging it out in front of everyone else. In the past, TV might have hosted a bust-up between two antagonists. But the spontaneous（adj.自发的；自然的），genuine row unfolding（unfold v.打开;呈现）in real-time in front of a mass audience: that's new.

And those exchanges often descend（ V.下降;下去）into the toxic（adj.有毒的）. The instant they shift to Direct Message mode一without an audience一they become calmer and more considered ,freer of performance and posturing. But on the platform, in public view, Lanier is right： even good people rapidly become “assholes”. If they have something else at stake—for example, their career prospects when they post on LinkedIn—the tend to behave better, he says.

Part of the problem is the lack of context. On social media, people too often approach a statement as if it is the very first that person has made ( unless, of course, they want to expose the tweeter as a hypocrite（n.伪君子）, by revealing the contradiction（n.矛盾;否认）with thoughts posted earlier). Sometimes the results are comic—when a bloke in the pub is telling a nuclear weapons engineer how nukes work—but more often it's just infuriating（adj.令人大怒的）. So you're denounced for “failing to address”x，when you have, in fact, been addressing x for years and, indeed, addressed it in a tweet posted a matter of minutes earlier. It9s partly this lack of context that explains the aggressive atmosphere. Those we know well need do little to gain our attention ； those we don’t have to shout and scream and swear to get noticed.

And all this is before you get to the proven, documented abuse and manipulation（n.操纵）of these platforms by people who mean us harm, as revealed by my Observer colleague Carole Cadwalladr in her expos6s of Cambridge Analytica and Facebook； witness the Russia-backed content that reached 126 million Americans via Facebook during the 2016 presidential election.

But the truth is, the problem lies not with abuse of the medium, but with the medium itself. Addiction was built into social medians design from the start—recall former Facebook president Sean Parker describing the “ little dopamine hit ” the product gives users to keep them hooked一and so too was the anger. The feedback algorithm rewards “engagement”，and a swift，vicious denunciation registers as engagement of a particularly intense kind. Lanier notes that an unintended consequence of Black Lives Matter was that, thanks to the algorithm, it connected its fiercest opponents with each other online, fuelling and cohering the resurgent white supremacist movement we see today.