By rights, on a bright Friday afternoon in late spring, Sumeja Tulic had every reason to relish walking the streets of New York, a city she moved to nine months ago from London for graduate school. “When the weather is good, it’s very hard to find a reason to be depressed or melancholic or dissatisfied with the city,” Ms. Tulic said.

Yet her time in New York has coincided with a season of ceaseless ugliness in politics and serial acts of terrorism around the world. “One day you laugh, and then you’re really angry,” said Ms. Tulic, a Bosnian-Libyan and a Muslim.

As she walked toward the subway station in TriBeCa on Friday, she hoped for a fair, fresh wind.

“I was saying, ‘Please, God, just something nice — I want to see something nice,’” she said. “Enough of this craziness.”

At the City Hall station for the R train, she settled onto a bench. It was just after 2 p.m. Only a few people were at the station. The space was quiet, the lack of noise and bustle a substrate for the events about to unfold. A man leaned against a pillar, the way anyone might, waiting for the train that would go uptown in Manhattan and later turn east for Queens. The stillness was interrupted with an announcement. “They said the next train was two stations away,” Ms. Tulic said. Another long moment, then out of the corner of her eye, she glimpsed the man at the pillar collapsing forward, but the movement did not register as much as the sound.