The modern English word secret comes from the Latin secernere, or to separate or distinguish. The prefix “se-” means apart, and “cernere” is to sift. To keep a secret, then, is to keep some particular bit of information sifted apart from a particular person.
As psychologist Art Markman notes at Fast Company, that’s one major reason for why keeping secrets is so difficult. Even if you’re the most loyal of friends, keeping something sifted is a cognitively demanding task, and our minds aren’t quite as nimble as we might hope for them to be. It’s a surprisingly complex maneuver: You have to keep in mind not only this privileged piece of information, but also what your conversational partner does and doesn’t know.
“Our minds have a limited capacity to process information,” Markman writes. “So if you’re engaged in a complex discussion, it may be difficult to keep track of what you’re allowed to say and what you aren’t, which can lead you to divulge information you shouldn’t.”
In other words, secret-keeping requires some mental multitasking. And the thing is, as one University of Utah study suggests, the people who multitask the most are the worst at doing so. Multitasking takes away bandwidth from what psychologists call “metacognition,” or your awareness of your own mental processes. “If you’re doing a lot, you have less attention to monitor your own activity, so you’re not aware that you’re missing some details,” Utah psychology professor David Strayer once told me in an interview. Strayer’s research was looking at how people text and drive, but a parallel process is happening when you’re toggling between thinking about what your conversational partner knows and what you’ve been sworn to not let them know.
But that’s not all. With secret-keeping, Markman says, there can also be a temptation to get a reaction from someone by telling them about something you know about and they don’t. It’s the same impulse, he says, that drives you to share insightful posts like this one with your friends or tell everybody how The Lobster was the cleverest movie you’ve seen in years (spoiler alert: It is). That’s the dual-pincered difficulty of keeping a secret: Doing so unburdens your mind from having to keep track of what other people know and don’t know (what a relief!) and gives you the oh-so-delightful social reward of surprising others — for better or worse.