This is Hidden Brain.
I'm shankar vedantam.
In 1965, Mark Rudd was an 18 year old freshman at Columbia University in New York.
America's military involvement in Vietnam was ramping up.
At first, Mark wasn't interested in much beyond his studies.
But before long, he was drawn in by the passion of his politically engaged peers.
He would later write, over beers or a joint, I'd listen to discussions about China's Cultural Revolution then just starting, and to Cuba's seven year old revolution.
It was thrilling to be with these people who are tapping into something so much bigger than ourselves, something so grand, so historic, remaking the world.
By the time he was 20, he had been elected chairman of the Columbia chapter of Students for a democratic society, or SDS.
In 1968, he led the student occupation of several university buildings.
He called his parents, exhilarated.
We took a building.
He exclaimed.
Well, give it back, his father told him.
But Mark was drawn deeper into radicalism.
Along with some friends, he formed a revolutionary band known as the Weather Underground.
The group sought to violently overthrow the government and instigated a string of bombings.
The violence gave Mark pause, but he felt compelled to continue.
I felt like a member of the crew on a speeding train, dimly aware of disaster ahead but unable to put on the brakes, he would later recall.
Decades later, Mark Rudd said he had feelings of guilt and shame about his actions.