Several years ago, the company I was working for reorganised itself to have a matrix reporting structure. In the process a few people were promoted to become project managers. One of them reportedly gave instructions to his team members without considering the consequences of their impact on other projects that some of these headcounts were also assigned to. His action upset another of his fellow project manager and embarrassed himself in the process. The other project manager was saying that power has gotten to the head of this new project manager!
A friend of my, Andrew Tan, relate to me a story about him getting promoted while working in the US. At that point his father told him that this. "It is very nice to be important. But it is more important to be nice." I find this advice from Andrew's father very meaningful.
