Years ago, Nicole Hallberg and Martin Schneider were coworkers at a small employment service firm.

Doing the same job in the same city at the same firm, one would think Hallberg and Schneider’s lives would be incredibly similar. And they would be, if not for one simple thing: their names.

Time and time again, the two would receive drastically different responses—thanks to each of their first names (Nicole’s traditionally female name and Martin’s traditionally male name). While they each had to deal with responses both from clients and from their “efficiency-fetishizing boss,” the language of those responses was drastically different. Martin shared just how unique communication could be for the pair in a story on Twitter that went viral because it highlights one of the most frustrating aspects of being a woman at work: sexism from clients. 

As Hallberg’s supervisor, Schneider was asked to look into what was taking her so long to work through customers. At first, he thought Hallberg was having trouble because she was less experienced than he was. But, as he dug into her workload, he started to notice that she had to deal with more belligerent, demeaning, mansplaining clientele.

Here’s what happened next as told by Schneider in a series of tweets: 

The simple act of switching names showed a clear difference in how one employee was treated over the other. In a Medium post by Hallberg, she shared her boss’s reaction to the simple social experiment. “There are a thousand reasons why the clients could have reacted differently that way,” [Schneider] said. “It could be the work, the performance … you have no way of knowing.”

The statistics on sexism in the workplace are alarming. Women get paid 77 cents on every $1 men make. Just 4 percent of S&P 500 companies have female CEOs. According to AOL Jobs, 83 percent of sexual harassment charges brought in 2010 were from women. And, in an experiment dealing with unconscious bias, “male applicants for a lab manager position in one experiment were hired more often and offered more money when their name was John as opposed to Jennifer—despite identical CVs.”

For Schneider, this simple experiment from “two bored coworkers screwing around while the boss was away” taught him to stop being part of the problem and to become part of the solution.

“I think a lot of people—primarily men, including myself—try to excuse or ignore our own sexist behaviors because we like to think of ourselves as ‘the good guy,’” he said. “So I think the takeaway here is to monitor yourself and other men around you … You’re not a bad guy for doing what you were brought up in society to do. You’re a bad guy if you’re made aware of it and you make no attempt to change your behavior.”