Before the Presidential inauguration ceremony the CIA briefed JFK on a secret plan designed during the Eisenhower administration.

The plan was to finance and train a clandestine army of Cuban exiles to invade Cuba.

JFK saw no treat in Cuba. He also had some doubts this was the right plan to overthrow Fidel Castro's dictatorship.

But JFK wanted to send a message to other communist powers like the Soviet Union and China. JFK also wanted to show skeptical Americans that he was dead serious about winning the Cold War.

So JFK gave the CIA the green light.

On April 17, 1961, 1,400 Cuban exiles invaded the Bay of Pigs on the south coast of Cuba.

But the attack was a clusterfuck of epic proportions. Everything went wrong. Castro's troops killed 114 of the invaders and captured over 1,100 men. The whole thing was over in 2-3 days.

JFK privately wondered, "How could I have been so stupid to let them go ahead?"

In 1973, Yale psychologist Irving Janis began researching the chain of events behind the Bay of Pigs invasion of 1961.

Janis observed the same kind of flawed group dynamics that he had discovered in other social psychological research.

Janis discovered that JFK and his advisors were victims of “Groupthink”. Groupthink is a psychological phenomenon in which a group of people strive for consensus at any cost.
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Arthur Schlesinger, Jr., one of JFK's advisers present at the meetings before the Cuban invasion, later wrote:

Our meetings were taking place in a curious atmosphere of assumed consensus, not one spoke against. Had one senior adviser opposed the adventure, I believe that Kennedy would have canceled it.
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We, humans, are social creatures. Our urge to belong and conform can make us ignore or override our own beliefs. It can make us adopt wrong behaviors or beliefs, just because they're popular. Just because "other people are doing it", we want to "get on the bandwagon", too.

In psychology this is called Bandwagon bias. Bandwagon bias is a form of groupthink and it can have a major impact in social and political movements.

When people have limited information about a specific topic, instead of "buying" information, they tend to follow signals from others. To save time. (Read Susil Bikhchandani, David Hirshleifer, and Ivo Welch, 1992).

The Bandwagon effect also explains how fashion trends start (D. Stephen Long; Nancy Ruth Fox, 2007).

A classic example of the bandwagon effect in action is when preference for a product increases as more people buy that product.

Apple became the World's most valuable company thanks to the bandwagon bias.

Remember all those crazy queues outside the Apple Stores a day before Apple released a new iPhone? It was a signal that Apple products became a popular status symbol for "cool people".
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