George Zimmerman faces charges of second-degree murder for fatally shooting Trayvon Martin in Sanford, Fla., on Feb. 26.

And though Zimmerman has yet to appear before a jury, many people have already judged him guilty, or not guilty.

Psychologists say this rush to judgment is part of being human, and we do it all the time. Think of Amanda Knox or Dharun Ravi, the Rutgers student convicted of spying on roommate Tyler Clementi, or even Dominique Strauss Kahn, the former IMF chief accused and cleared of raping a New York hotel maid.

"Judgments help us make sense of things. We tend to be uncomfortable if we don't know what to think," said Nadine Kaslow, a professor and chief psychologist at Emory University's Department of Psychiatry and Behavioral Sciences. "On the other hand, sometimes we quit seeing the whole picture, quit seeing the complexity of the story and rely on our biases."

It's a tendency we can't help, said psychologist Daniel Khaneman, Nobel laureate and professor emeritus at Princeton University.

In his book, "Thinking, Fast and Slow," Kahneman describes the brain's innate tendency to function in two ways: There's fast thinking, the intuitive, emotional gut reactions formed seemingly without effort, and slow thinking, the deliberate, rational musings that try to take all facts and perspectives into account.

It is the fast thinking side of the brain that works from emotions and preconceptions to form our own story for a particular event.

"We couldn't get by without fast thinking. We can't always analyze evidence over time. We have no choice but to operate mostly in fast thinking," Kahneman said. "It does occasionally get us into trouble."

Kahneman said fast thinking probably played a role not only in how people see Zimmerman's defense but also how they interpret Zimmerman's actions that February day when he shot Martin.

The shooting was likely "emotional, very fast and not based on careful consideration of the costs and benefits and risks," he said.

Whether thinking is fast or slow, judgements have a neural basis. Liane Young, an assistant professor of psychology at Boston College, studies the neural hardware that's active when the brain is making moral judgments. In 2010, she and her colleagues looked at how a certain area of the brain -- the right temporal parietal junction -- responds when weighing right and wrong.

Young said brain activity in the region changed depending on how a person viewed the mental state of a person who wronged or harmed someone else – whether their actions were accidental, intentional or malicious.

The area, located on the right side of the head just above the ear, was most active in people who were more sensitive to the mental state of the person in the wrong.

"People who have higher levels of activity in this region tend to process mental state information more deeply and rely on it for moral judgment," Young said. And those people were more likely to forgive a person who harmed someone else.

While the judge and jury who decide Zimmerman's fate will have to consider the facts and not be swayed by outrage and emotion and personal bias, the facts are not so important for the rest of us, said Kahneman.

"Most of us don't have much reason to revise our opinions. We're not strongly motivated to find the truth," he said. "We simplify reality. That's quite a comfortable convenience."