We’ve all been there — sitting in a restaurant, on a train, or at a store, quietly judging someone else’s behavior.

But experts say that quick tendency to judge others may do more harm than we realize —especially to our own mental health.

Editor’s Note: Tired of Mental Fatigue? Here's How to Get Your Edge Back

In fact, research shows people often form impressions of others almost instantly — sometimes in as little as 100 milliseconds — based on facial expressions and behavior alone.

According to brain health expert Dr. Gary Small, director of behavioral health breakthrough therapies at Hackensack Meridian Health, these snap judgments are not only common, but largely unconscious.

Special: Worried About Forgetting Things? Try Dr. Blaylock's Brain Boosters

“We all do it,” Small told Newsmax’s “National Report.”  “And what happens at an unconscious level when we observe traits in others that we share and dislike about ourselves, that's when we're being judgmental.”

Most of the time, he explained, people aren’t even aware they’re doing it.

Editor’s Note: The Walking Method Doctors Say Protects Your Heart, Brain, and Waistline

“Most of the time…it's just completely out of our awareness, and we make these judgments very quickly and automatically,” he said.

While judging others may initially feel justified, that feeling doesn’t last — and may actually backfire.

Neuroscientists have found that a judgmental mindset can negatively affect mood and overall mental well-being. A study from the Sapienza University of Rome examined how judgmental attitudes impact emotional health, looking at factors such as worry, age, and gender.

“They found that a judgmental attitude predicted negative moods more,” said Small, who is also editor of Dr. Gary Small’s Mind Health Report. “It was the strongest predictor of depression and anxiety.”

So, what can people do to break the habit?

Small says the first step is awareness — catching yourself in the act.

“You need to be aware of when you're being judgmental of others and ask yourself, does that remind me of my own imperfections?” he said.

From there, shifting perspective can make a big difference.

“With that awareness, you can substitute that judgmental attitude for an empathic one,” Small explained. “And that will not only boost your level of compassion, it will make you feel better and less likely to get depressed and anxious.”