'Put a smile on your face' says dad in viral post

Before you open the door, "put a smile on your face."

That's the advice of one North Carolina dad of four whose simple post has gone viral on Facebook.

"It doesn't matter how your day went. Or what you're doing next. Or if you're starving," Benjamin Holmgren wrote earlier this month. "For 30 seconds, at least pretend that you're elated to see them. Make them feel like you were looking forward to getting back home. After all, they're your favorite people in the whole world. I hope."

Holmgren credits author Brene Brown for the idea. His post has been shared almost 300,000 times.

He told "Good Morning America" he never expected it would go viral.

"I've been writing consistently for years [on LinkedIn] and have had plenty of posts that nobody cared about," he said. "This one really struck a chord at the right time."

He said that in "a day and age of noisy internet trolls," the feedback on his post has been overwhelmingly positive.

"I love that people are taking the encouragement and doing something about it," Holmgren told "GMA," and it's making a difference in their lives. Just like it has in mine."