Over the last two years, at least five young activists who gained national prominence amid the Black Lives Matter movement have died. The causes range from suicide to homicide to natural causes. Most recently, Muhiyidin Moye, a well-known activist from Charleston, was fatally shot last month in New Orleans in a crime that remains unsolved.

The deaths have their own unique causes. But with each fallen comrade, activists are left to ponder their own mortality and whether the many pressures of the movement contributed to the shortened lives of their colleagues.

Along with the long hours, constant confrontation and frequent heartbreak they experience, activists work for little or no pay and sometimes struggle for basic needs like food and shelter even as they push for societal change.

An essential part of activism these days, those on the front lines say, is ensuring that they and their comrades work through all the stress, whether it’s with meditation, therapy or just taking breaks from the struggle.

“It’s much more front and center than it ever was when I was coming up as a young organizer 20 years ago,” Cat Brooks, an Oakland-based activist, said of self care.

In many ways, Ms. Garner’s story represents the perils activism can inflict on a life.

She grew up poor in New York. Her father died a very public death in 2014, one she would witness through bystanders’ videos of a police officer on Staten Island confronting her father on the street, putting him in a chokehold and tackling him to the ground. Mr. Garner lost consciousness and died after crying out in distress, “I can’t breathe.”

Ms. Garner’s activism, like that of many new to a cause, was initially driven more by passion than polished ideas. She held weekly protests on Staten Island, demanding that the officers involved be punished. Yet she doubted that race played a role in her father’s killing, she said in a CNN interview.