SINGAPORE - After walking down nearly 40 flights of stairs, exiting the burning North Tower of the World Trade Center, and crossing an overhead bridge, Singaporean Rachel Yager finally stopped and turned to look back at the building.
"There was this big hole. I thought, 'they can never fix that hole'," she says.
This enduring memory of the Sept 11, 2001 attacks has become, for the 53-year-old, a metaphor for not just the United States and the world but, in some ways, her personal outlook.
"How do you fix something created by so much hatred over so many years?" she muses.
She adds: "I felt that hatred at the time - how I couldn't do much about it, and how it had emptied out my sense of innocence.
"I imagined my whole life would be peaceful. I never thought I would be in a war; or that someone would want to kill me, or at least put me in a group of people that they felt should be targeted and gotten rid of."
The consequence, says Dr Yager, who has worked and lived in the US for 23 years, is an ingrained cautiousness and a notion of the world as no longer being safe: To this day, she prefers taking a taxi or an Uber instead of the subway.
Twenty years ago, when terrorists hijacked and crashed two planes into the World Trade Center's twin towers, she was working for Lehman Brothers on its 38th-floor office in the North Tower.
Aware that something terrible had happened above - the plane had crashed between the 93rd and 99th floors - Dr Yager took the stairs and escaped the building. Her legs were shaky, but she decided to make the three-hour walk home - in her high heels initially, before stopping to buy sneakers later.
Her neighbourhood on New York City's Upper East Side was peaceful, she recalls, "like nothing had happened". Her husband, American researcher Ronald Yager, was waiting at the door and in tears.
That night, the couple went out for dinner. "Everything was not quite right, you could feel that the whole city was very quiet," says Dr Yager, who went on to start her own management consultancy. "And I can never forget - as we were sitting at the restaurant, there were big trucks carrying the debris from the World Trade Center site, going back and forth."
Despite her general wariness, Dr Yager stresses that she does not live in constant fear of invisible dangers.
"I got a chance to live longer, so I do think about why, and what I should be doing more," she says.
"Some things remain beyond my control. But what I say, whether I choose to help people - that's the least I can do, to try and make sure future generations don't have a 9/11 of their own."