“How I distinguish a weak tie from a stranger is that there’s mutual recognition,” says Gillian Sandstrom, a senior lecturer at the University of Essex who has studied the effects of weak ties. “You don’t have to know the other person’s name, but you have to have seen them and know who they are.”

Sandstrom co-authored a 2014 study titled, “Social Interactions and Well-Being: The Surprising Power of Weak Ties,” which emphasized the significance of these underrated connections. “These kinds of minimal interactions with people make us feel good—like we’re connected to people,” she says. “It makes us feel more trust in the world and more of a sense of community. I think that’s something humans really need. We need to feel like we’re part of something—that we belong. And we suffer all sorts of negative consequences when we don’t feel that.”