In one example in my career, a big employer was trying to change its culture, and set up a group to change its practices. Hired a lot of good, pretty expensive people. And it all worked well for a while, until one person decided that grass was greener somewhere else. Losing a teammate led to another, then another. The people that left had new employers, and happily recommended them. Others that were happy before were less happy with enough good coworkers gone, as management did nothing to special to keep them. In 6 months, everyone in that change initiative, and a lot of other employees they had contact with, were all gone. They ended up having to outsource everything said department was doing, because too much of the knowledge and expertise had left.
So beware when people leave, because coworkers leaving can a very common trigger for shields to go down.