There are quite a few things, some of them subtle, that really change once you're in a leadership role. The frequent example I see is that people don't realize that if they are in a leadership role, then there will be decisions they make which people on their team do not like. That's ok. It's not the job of the leader to win a popularity contest, but rather to try to do the best thing for the individual team members, the team, and the company itself. A lot of people have a tough time with the fact that others won't like their decisions, but that's a critical thing to digest for those who are going to be effective leaders.
Hmmm. Older than I remembered. But a few of the recommendations in it have stuck with me and it's been as helpful as anything I've read on the topic.