According to a study by BCG, 85% or companies have undergone a major transformation in the last decade (https://goo.gl/Cjya3w). Worryingly, the same article noted that nearly 75% of the transformations failed to improve business performance, either short-term or long-term!
HBR found that a key reason was the fear and insecurity that caused people to keep behaving in ways that did not serve them well, even when they understood this to be the case.
Leaders can change policies, strategy, etc., but until they change people's attitudes and thinking, and address their fears, it will always be difficult to make change stick. Of course, the first person that must change is the leader himself.
Remember that leadership isn't just about driving change; it's about taking people with you and maximising their contributions.