In The World is Flat, what does Friedman mean when he says, on p. 21, that "change is hardest on those caught by surprise?"
What Thomas Friedman means when he says that "change is hardest on those caught by surprise" is that people and businesses can adjust to change if they anticipate it. If they do not anticipate it, they will have a hard time adjusting and will be badly hurt. To see how this is so, let us simply think about a hypothetical case of two individual workers.
Imagine two people who have been working in a textile factory in South Carolina. Both are 40 years old and have been in the same factory for 20 years. One of them anticipates that their factory is going to close in a few years because of foreign competition. That worker goes back to school and takes night classes that allow her to get a nursing degree. When the plant closes, she is eventually able to get a job in a hospital. The other worker assumes that the plant will go on for another 20 years and that she will never need to change careers. She does not plan for a change. When the plant closes, she is left with no skills that will be valuable to employers in other industries.
In this scenario, the worker who was caught by surprise by change was more badly harmed by that change. This same logic can apply to companies, which can go broke if they do not anticipate changes. This is what Friedman means by the quote cited in the question.