September 29, 2016 5:39 AM EDT

In today’s digital world, we’re often expected to be on email at all times. Recent studies show that office workers spend almost a third of their workday reading and responding to messages. This constant connectivity can be harmful: scientists have established a clear link between spending time on email and feeling stress.

So why do we do it? Many of us are addicted: checking email activates a primal impulse in our brains to seek out what behavioral psychologists call “random rewards.” Imagine email as a slot machine. Most of the time when we “pull the lever” to check our messages, we get something bothersome–a complaint from a client, a request from our boss. But every once in a while we get something exciting–a note from a friend or (if we’re really lucky) a video of goats jumping on things. It’s those random rewards, mixed in with all the mind-numbing updates, that we find so addictive. Moreover, the mere fact that someone took the time to write us an email activates a deep-seated social behavior: the desire to reciprocate like with like, which can create unrealistic expectations for how much we can take on.

But striving for inbox zero is, of course, a Sisyphean effort at best. Just when you think the task is complete–ping!–a new message rolls in. What can we do about it? With email–as with everything else in life–we must learn to say no to some opportunities, in order to say yes to our priorities.

Glei is the author of Unsubscribe: How to Kill Email Anxiety, Avoid Distractions, and Get Real Work Done

This appears in the October 10, 2016 issue of TIME.

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