The U.K.'s historic vote to leave the European Union, many people believe, was driven by opinions on immigration.
And it likely was influenced by the way people are psychologically wired. Analysts on Friday repeatedly cited voters' emotions as the driver of Brexit. Many people may have voted with fear or anger as their primary motivator, even though it had been well known that leaving could have widespread consequences, including economic turmoil and adverse effects on public health.
"We are leaving the EU and entering a dark and uncertain period,"Gary Younge, editor-at-large for The Guardian, wrote after the "leave" vote won Thursday's referendum. "Offered a choice between fear of the unknown or fear of the foreigner, fear inevitably won. Britain lost."
Why do we fall for fear or anger-based arguments?
Brexit supporters argued for strict controls on immigration, and said Britain's membership in the EU led to loose borders. The EU's free-movement policy allows European nationals to live and work in any EU state without a work permit.
The anti-immigration outcry was heightened by the surge of migrants and refugees, including many from the war-torn Middle East. More than 1 million refugees have poured into Europe, primarily in the past year.
The vote shows deep worry about immigrants and what they mean for job security, safety and economic growth -- fears that many consider xenophobic.
It's not hard to see the fear in Brexit supporters' tweets:
Political language that incites fear by spotlighting terrorism risks, for example, can sway conservative voters, researchers say. Fearful voters are prone to choosing an outcome based on new information, often abandoning their previous loyalties or affiliations.
Many Brexit voters may have felt neutral or even uninformed about the EU, the alliance they voted to leave. The day after the referendum, many UK residents were Googling, "What is the EU?"
Those who are angry are less likely to be invested in the political status quo and the options available to them. Studies show angry voters tend to be partisan and unreceptive to points that conflict with their own, according to the American Psychological Association.
Emotions can rule in the voting booth
Psychologists are increasingly finding that emotions can play a major role in elections.
"Thinking and feeling go hand in hand. In any decision-making -- including political decisions -- how people feel about the information they're being given is important," Tereza Capelos, an expert in political psychology at Surrey University, told the BBC last year. "Emotions help people make decisions."
Perhaps that's why the Brexit decision was shocking. Those arguing for Britain to remain in the EU presented sensible reasons (public health, scientific research, the environment, the economy). But many people rejected those rational views and went with emotion. And for many, the result was devastating:
Europe isn't the only place where fears and frustrations run amuck and influence voting. It's happening in the U.S. as well, with Donald Trump riding his proposed ban on all Muslims from entering the U.S. to the Republican presidential nomination.
Of course, human nature is a complex construct. There are a lot of other psychological factors that can inform a person's vote, from attack ads to a candidate's physical appearance. But they all influence how an individual feels. That means emotions have a very large impact on important choices, like the Brexit referendum.
Fear and anger can have a lot of agency -- but they don't always make the best decisions. (You listening, America?)