Everyone needs attention, like we need to eat. This is not controversial, nor is it hard to understand. But the idea must be slippery, because it will not stick. If we could keep in mind that people need attention, it would change the way we see almost everything they do, from art to crime, from romance to terrorism. And we must. Facebook alone harvests and sells the attention of 1.4 billion people every day. That’s about a fifth of the world. This alarms some people, and it is a big change. But we can’t know what to make of it until we understand what people need attention for.

Attention is other people thinking about you, and if there were ever humans who didn’t need it, they are now extinct. “Attention is one of the most valuable resources in existence for social animals,” says Dr Geoff MacDonald, a psychologist at the University of Toronto with an interest in human connection. “It was literally a matter of life and death. The people who didn’t feel good around others, or didn’t feel bad when they were separated from others, wouldn’t have the motivation to do the things that are required to pass their genes down the generations.”

Specifically, people have been shown to need a type of attention that psychologists call belonging. Abraham Maslow put belonging into his famous hierarchy of needs in 1943. In 1995, Roy Baumeister and Mark Leary concluded in their paper The Need to Belong that the available research did indeed show that everyone has a “strong desire to form and maintain interpersonal attachments”. In particular, they identified that belonging means getting positive attention from people who know you well.

This isn’t hard to understand either. Someone who thinks well of you is more likely to cooperate with you. Or even mate with you, if you’re lucky. But their opinion only really counts if they’ve spent a lot of time with you, because that makes their idea of who you are more accurate, and only accurate approval is secure. “If you feel like you’re accepted for false reasons then that’s bound to create anxiety,” MacDonald says.

People who feel they don’t belong suffer terribly, and experience health problems comparable to smoking or obesity. They are the 18% of British adults who reported always (4%) or often (14%) feeling lonely, in a study published last year by the British Red Cross and Co-op. There are more lonely people in Britain than live in London. The problem is now obvious enough for the government to appoint a so-called “minister of loneliness”, Tracey Crouch.

The word loneliness is a good description of the feeling, but not its cause, which in reality has little to do with being alone. According to the report, just 22% of people who live alone feel lonely always or often, not much more than the 18% national average. Among 16-to-24-year-olds, on the other hand, the proportion is 32%. This shouldn’t be surprising. “Generally, loneliness seems to be a matter more of a lack of intimate connections than of a lack of social contact,” Baumeister and Leary wrote. Lonely people lack attention that is positive and accurate, in short.

So why don’t they ask for more? Because attention can be harvested only from the minds of other people, and high-quality attention won’t come by force. “In anthropological terms, it’s a gift economy,” says Dr Amy Pollard of the Mental Health Foundation (MHF), a charity that campaigns on loneliness. “You’re creating bonds of reciprocity, which is where the belonging comes from.” This means you only have as much high-quality attention as people want to give you. And asking for more – attention-seeking – is a signal that, in your case, they don’t want to give much. This isn’t fair. Nor is it reliable. (People can misjudge you.) But the idea that lonely people don’t deserve attention comes to us instinctively, as when we see an empty restaurant with a busy one next door.

Some lonely people themselves conclude that they aren’t worthy of attention, and withdraw from the world still further. Others search for a feeling of belonging, not always in the best way. Seek positive attention too openly and you get called “narcissist”. Seek attention from your family with great displays of wanting to be ignored, and they’ll put you in a Jewish mother joke. There are many ways of asking without asking, if we are prepared to notice. Why, for instance, is it taboo to suggest that people who self-harm, or have anorexia, might want attention? Is that not a source of pain worth taking seriously?

One way to seek attention is to do something that gets lots of it – art, politics, crime, journalism maybe – but that seems to have another purpose. The purpose matters. Otherwise you risk the special scorn reserved for people who are “famous for being famous”.

When Jamie Jewitt entered Love Island on ITV2 last July, he was depressed. A successful model based in New York, he had returned to Essex to live with his parents, then did nothing for years. His family all but forced him to join the show, aged 27, in the hope that it would shake him from his torpor.

In modelling, Jewitt explains over coffee, Instagram is non-negotiable. “You wouldn’t get work,” he says, “if you didn’t get a following.” In practice, this is quite easy for a model to do: just feed the public appetite for carefully posed and manipulated “snapshots”. Over time Jewitt gathered 13,000 followers. He enjoyed their compliments and exchanged messages with some. It was almost friendship. “You tell yourself you’re getting the real thing,” he says, “but it’s so hard to tell the difference.” He found he’d switch between bursts of activity and guilty silences. “I felt like a hypocrite, like a sellout. It was a big part of why I got unhappy. You feel isolated, but you don’t know why.”

When arriving on Love Island, all contestants must surrender their phones. Inside, there are no TVs, no iPads, no contact at all with the outside. “You have to talk to people,” Jewitt says. “Get to know them, make friends.” What we never saw on Love Island were the hours upon hours of intense conversation. “On mine and Camilla [Thurlow]’s dates, all we’d talk about was books,” Jewitt recalls, “and none of that made it! People don’t want to hear that crap, do they?”

It’s funny that it took a reality show to make Jewitt live authentically again. “After two days I would wake up in the morning feeling so relieved,” he says. “It was unbelievable. A fresh start. The sad thing was I could have done it at any point on the outside.” Today he and Thurlow are still together, and the islanders remain close friends.

Now Jewitt has 801,000 Instagram followers, and mostly promotes good causes. These posts aren’t popular. “When I post about the things I care about, I lose close to a thousand followers,” he says. So far he has lost around 20,000 since his peak after Love Island, and has come to take a strange pleasure in the process. “I wouldn’t want it any other way,” he says, “because I want the people who follow me to know who I am, and like who I am. I’m trying to depict a more real version of myself.”

Social media is bewitching because there’s time to lie, not like in real life. The opportunity for positive attention is enormous, but accuracy is the price. “When you present a curated version of yourself to the world, any approval that you get is not for your full and whole self,” MacDonald says. As Jewitt found out, this corrodes your feeling of belonging.

We don’t know yet whether social media makes people lonely. Even if it does, we should remember that it is also useful to keep real friendships going. But an MHF survey last month found that 30% of young Scots say social media makes them feel isolated. The 2015 Pisa schools report showed a dramatic fall across the developed world since 2012 in the number of children who would say that “I make friends easily at school”. By a small margin, those who use the internet the most were also most likely (17%) to say that they felt lonely – although we don’t know which was causing which, if either. We also don’t know how much of their time online was spent on social media.

Even if offline time is good for you, it can be stressful, which might make people hide behind their screens. “I always say to my students,” MacDonald says, “‘If only in real life we had a backspace button.’ But no. Once you say something, it’s out there. You don’t get that kind of control.” Until recently, in other words, most of us were simply too socially clumsy to avoid being ourselves.

For some people, usually those who had a hard time growing up, this stress can be unbearable. A fixed belief that you aren’t worth liking creates a loneliness and craving for attention that they struggle to satisfy. If desperate enough, they may even force other people to notice them, preferring to be hated than ignored. These people are unhappy, and can be dangerous. They commit crimes of attention.

Broadly speaking, there are two types of stalker. “One is the intimacy-seeking stalker,” says Dr Brian Spitzberg, a leading authority on stalking behaviour at San Diego State University. “They are trying to get back to a person who has rejected them in some way.” Often these people used to be in a relationship with their victim, the end of which they cannot accept. “They are enveloped by the sense that this is the right person for them. They feel injured and rejected … but underlying that is a desire for the attention they think they deserve.”

The other type he calls “public figure stalkers”, who usually do not know their victim personally, but pester them in order to achieve a goal of some kind. “There is something they want done that they perceive public figures aren’t doing,” Spitzberg says. “Some of them simply want someone in an authoritative position to pay attention to their voice.”

Loneliness is common among stalkers. (One of them narrates my novel, for which this article is in part a bid for attention.) However, attention is not often considered to be their motive. What a stalker wants seems obvious: to be part of their victim’s life. Their behaviour is irrational; it only makes the victim reject them even more, but the stalker either insists that the woman (about three-quarters of the time) will change her mind, or persists in a spirit of revenge. And he does become part of the victim’s life, of course. A big part.

After a firm rejection, the approach most experts recommend is to ignore the stalker. They work on the basis, as Spitzberg puts it, that “any kind of attention is still attention”. With this in mind, stalking behaviour seems half-rational in someone who is desperate for a feeling of belonging. Certainly most stalkers are not mentally ill in a way that a psychiatrist would recognise. According to Spitzberg, only 30-50% of all stalkings that become criminal cases can be traced to some kind of diagnosable disorder. Among intimacy-seeking stalkers, it’s even less. “Most intimacy-seeking stalking is something that almost anyone is capable of,” Spitzberg says, “if they meet the wrong person under the wrong circumstances.”

Sadly, some people feel not just ignored by their ex, but ostracised by the whole world. For them, life with almost no attention is sheer torture. A recent workplace study in Canada found that ostracism was worse than the negative attention of being bullied. The work of Professor Kip Williams at Purdue University in Indiana shows how ostracism causes pain, and can lead to antisocial behaviour. Another Mark Leary study shows it is a key factor in school shootings.

Like stalking, this is a crime that seems utterly irrational. Usually it suffices to say that the killer was angry, perhaps just insane. They are always lonely. Spree killers are fond of leaving documents that explain their feelings. Seung-Hui Cho (Virginia Tech, 2007) claimed he was bullied, which baffled those who knew him. Elliot Rodger (Isla Vista, 2014): “I felt depressed because I wanted sex yet I felt unworthy of it”. Often a grotesque spirit of belonging exists between them. Vester Flanagan (Moneta, 2015) was a fan of Cho (“That’s my boy, right there”). Matti Junahi Saari (Kauhajoki, 2008) and Pekka-Eric Auvinen (Jokela High School, 2007) swapped videos on YouTube. Auvinen quoted the manifesto of “the martyrs Dylan [Klebold] and Eric [Harris]” (Columbine, 1999), who also inspired Todd Cameron-Smith (Alberta, 1999), Adam Lanza (Sandy Hook, 2012) and everyone else. Needless to say, if they hadn’t killed anyone, we would have paid less attention to their feelings.

There was a time when spree killing almost did not exist. Guns existed. So did bombs and knives and vans. So did violent and disturbed people. Indeed the world is now generally less violent than it used to be. Yet spree killings grow more frequent. A study at the Harvard School of Public Health found that mass shootings in the US in which at least four people died occurred, on average, once every 200 days between 1982 and 2011. Then once every 64 days between 2011 and 2014. Eighteen of the 30 deadliest mass shootings in the US since 1949 have occurred in the past 10 years, including all of the worst five.

What else can we call these but crimes of attention, made possible by new media? Filmed on camcorders, then on phones. Seen live around the world. Stored on Wikipedia and YouTube for posterity. Where would you have found a copy of a killer’s manifesto in 1990, let alone a video? The truth is that if you want the world’s attention badly enough, you can have it tomorrow. It is easy. Before the internet, it was not.

Jihadists love to leave speeches too, but theirs claim grander motives. Their killing sprees, they say, are part of a plan to reach paradise and bring about the triumph of their beliefs. Yet many of them hardly live with the piety they die for. Shehzad Tanweer, one of the London tube bombers, had a secret girlfriend. Amedy Coulibaly, who attacked the kosher supermarket in Paris, kept paedophile material on his computer. According to Demos interviews with 62 former jihadists in 2010, they “had a simpler, shallower conception of Islam than [nonviolent] radicals”. Does it seem likely that they were forced into violence by their devotion to scripture? Or is it more plausible that their violence, which obsesses the world, feeds a craving for attention that they clothe in phoney zealotry?

It is hard to imagine crimes of attention disappearing, but admitting that’s what they are should help. Perhaps then we’ll stop rewarding criminal behaviour with so much of the attention that it seeks. There are other simple solutions to our attention crisis. Ideas like the Big Lunch, or the MHF’s “Tea and Talk” events may improve access to high-quality attention by helping people get to know each other better. Eventually the moment may come when we are officially urged to get a minimum dose of offline conversation every week, like exercise or our five-a-day. When we talk more freely about our attention-seeking, maybe then at last we’ll get the attention we need.

•Consent by Leo Benedictus is published by Faber & Faber (£12.99). To order a copy for £11.04 go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99