On October 14, 2003, Steve Bartman was escorted by ballpark security from Wrigley Field. He wasn’t a rowdy fan nor had he started a fight. He had innocently reached for a foul ball hit down the third base line and disrupted a potential catch by Chicago Cubs outfielder Moises Alou, embroiling Bartman in a terrible case of mass emotional contagion.

Emotions are contagious—hang around a smiling, happy baby and you can’t help but smile yourself. Spend time with an anxiety-ridden person and you’ll find yourself biting your own nails and tapping your toes. Emotional contagion is the tendency to catch and feel emotions similar to those around you. It’s been around since before our ancestors invented the first language.

When Moises Alou’s potentially game-making catch was ruined by Bartman’s attempt to snag a foul ball, Alou understandably reacted with extreme frustration, anger and contempt. He threw a tantrum on the field yelling at the fans, at Bartman, slamming his glove down on the ground and angrily gesturing at the crowd.

The brain’s Mirror Neuron System (MNS) interprets the body language, pupil movements, vocal tones and facial expressions of those around us. In turn, we begin to mirror those same sentiments with our own physical and facial movements. When Moises Alou reacted as he did, even those who couldn’t hear or see him but heard the description of his reaction began to mirror his sentiments and direct them, too, at Bartman. As a result, the normally friendly Chicago Cubs fans became an angry mob.

For the remainder of the game, Bartman endured jeering from those within and outside of Wrigley Field. The crowd chanted derogatory names, threw pretzels, hot dogs and beer at the Cubs fan shouting, “We’re gonna kill you!” as he was eventually led from the ballpark by security.

But what if Moises Alou had controlled his temper? Instead of being angry for a period of minutes, what if he’d shown his frustration and then visibly moved on, refocused on the game?

Whatever the reason, we’ve all experienced moments of duress, stress and negative emotions at work. Sometimes we breeze through the tough times. Others, we become mired in a negative funk. Like a junkyard dog that couldn’t leave an open can well enough alone, our noses are stuck and all we can do is wait for someone to help us.

Unfortunately, negative emotions are easy to catch. That’s why it’s important to learn to be aware of how you’re acting and what you’re saying when you’re having a bad day. You may pass it on to others. Consider how you feel if the boss scolds you or if you’ve had fight with a coworker. Your feelings become a distraction and you’re less productive.

To combat the blues, “You don’t need to try to feel positive,” says David R. Hamilton, PhD. “Just recognize that your body language and facial expressions reflect mood, so use these as tools.”

“Lift your shoulders back, breathe deeply and easily and smile if you can. With any luck, [the MNS of the coworker] will be able to mirror you,” says Hamilton.

After Moises Alou’s temper tantrum in left field, shortstop Alex Gonzalez misfielded the ball (a rare thing for the Cubs player). Had Gonzalez properly fielded the hit, the Cubs could have ended the half-inning with a double play still ahead by two runs. Instead, the focus remained on Steve Bartman as fans became more and more agitated.

The focus had completely shifted; distracted by their rage, anger, disappointment and anxiety the players and the Cubs fans directed a portion of their energy at Steve Bartman, instead of where it should have been: the game. The Cubs lost the game 8-3 to the Florida Marlins, who went on the win the world series that year.

The next time you’re angry, anxious or just not having a good day, remember how you’re feeling will spread to those around you. Though it may be unintentional and completely natural, it can still steal the show.