One of the things you tend to hear in law school and in business school is that predictability tends to bring stability. The outcome of the law tends to be predictable, though problematically less so. The outcome of economic policy tends to be predictable. If a Republican is President and the Supreme Court leans right, the variables tend to go a certain way. If the President is a Democrat and the Supreme Court leans left, the variables tend to go a different way.
You may dislike the direction and trends, but they are predictable. Consequently, businesses can plan ahead. They can find safe havens. They can move assets. They can use the predictability for their own stability. Other nations too can plan and predict.
The global economic systems in particular dislike the lack of predictability. That is why this statement from Secretary of Commerce Wilbur Ross is so troubling for big businesses, institutional investors, and global trade representatives. From Meet the Press:
You may applaud the President being able to throw everyone off his game, but the markets do not tend to reward arbitrary and capricious behavior, which is what this looks like. You might say it is great the President is doing this. But by doing either the tariffs or just leaving it to a guessing game, the President is introducing unpredictability and is so introducing instability into the systems that keep the global economy on course.