Discussing mental health at work just got a little less taboo.

It’s all thanks to a conversation sparked by an email one CEO wrote that went viral. Washington Post called it the “mental health email shared ’round the world.”

In case you missed it, here’s how it all went down.

Olark developer Madalyn Parker sent an email to her team letting them know she was taking a couple sick days to focus on her mental health. CEO Ben Congleton responded to Parker with the following message:

I just wanted to personally thank you for sending emails like this. Every time you do, I use it as a reminder of the importance of using sick days for mental health — I can’t believe this is not standard practice in all organizations. You are an example to us all, and help cut through the stigma so we can all bring our whole selves to work.

Parker wanted to give Congleton props for his note, so she asked if she could share a screenshot of the exchange on Twitter.

Nearly 16,000 retweets later, it’s clear this has struck a chord with many. It sparked a conversation about de-stigmatizing mental health in the workplace. “I wanted to call this out and express gratitude for Madalyn’s bravery in helping us normalize mental health as a normal health issue,” Congleton wrote in a response on Medium.

Many responded by sharing their own experiences of being chastised by their employer or looked down upon for mental health challenges. Countless reactions and articles have seen been written on the topic, and rightfully so. Nearly 20 percent of workers say mental health issues such as anxiety or depression made doing their jobs more difficult, Washington Post reports.

Congleton’s commitment to creating a healthy workplace culture has been celebrated in publications far and wide. His message was empathetic and heart warming and stigma-crushing and so many other adjectives at once. I’m not discounting any of that in the slightest. The real reason, however, that I found the exchange so powerful is what compelled him to write that email in the first place.

The leadership lesson hidden between the lines

Here’s another reason Congleton’s leadership skills are top-notch. No one else ever needed to know he wrote that email. He didn’t need the world — or even other employees at his company — to pat him on the back for being such a great guy.

While the email ultimately went viral and thousands of eyes have now seen Congleton’s words, he didn’t do it for the exposure. That’s because leaders lead even when no one’s looking.

Whether you’re in the C-Suite or are the CEO of the company, it’s your job to rally your team or entire company. It might seem most effective to put yourself in the spotlight by sending company-wide emails or calling all-hands meetings. Then more people can absorb your message at once.

Think about it. Congleton could have done just that. He could have simply hit “reply all” and sent the exact same message. More people would have seen it, and more people likely would have praised his actions.

But he didn’t. In his simple decision to respond to Parker privately, Congleton reminds us all of one trait many truly great leaders possess. They lead one-on-one just as often as they do in front of a crowd. When the doors are closed. When no one’s watching.

They don’t lead for the glory. They lead for the good of the company and the good of their employees, in whatever form that may take.