A behavioral economist says no one knows how to fix the most damaging effect of killing time on Facebook

At this point, it's something of a cliché to say that spending time on social media can be dangerous.

People are generally poor judges of how much others are struggling - and the deluge of engagement rings and newborn babies and grad-school diplomas can suggest that everyone else's life is hunky-dory, while you're the only one dealing with marital problems, or debt, or even boredom.

Ask Dan Ariely, a professor of psychology and behavioral economics at Duke University, and he'll tell you that this problem isn't going away anytime soon.

Ariely is the author of a new book on human motivation, "Payoff." When he visited the Business Insider office in November, he told us that spending time on Facebook and other social-media sites can often be demotivating and can make users feel inadequate, though he said he hasn't seen much research on the topic so it's hard to quantify the effect.

The real issue is that it's almost impossible to find an antidote to this demotivating effect.

"I don't know if we could force people: Every time they post something good on Facebook, they have to post something sad as well," Ariely joked.

He went on:

"I don't know if we have another social network for just the difficult things in life. I don't know if we do this by getting people to have more deep-meaning conversations with the people that they care about and know well, so we don't have this illusion.

"It's not clear to me what's the answer, but if the world moves more and more to just portraying the beautiful part of it and not the challenges, I don't think it's a development in the right direction."

One potential solution may be to spend more time directly engaging with people on social media, since a 2015 study found that using Facebook passively - like scrolling through your newsfeed without posting anything - can make us less happy.

Still, that same study found that passive Facebook use is more common than active Facebook use.

Perhaps over time, social media will become more of a platform for emotional expressions of all kinds. Or, perhaps users will become more sensitive to the fact that what they see on social media is hardly reality - and that there's a good chance other people's emotional lives mirror their own.