Accepting that the team will design differently than you would
The hardest adjustment was accepting that my team would make different design decisions than I would have made, and that this was fine. Not just tolerable, but actually correct.
A designer I hired had a different approach to information density than I did. Where I would have reduced the number of elements on screen, she would keep them and use hierarchy to manage the complexity. Her approach was not wrong, it was different, and it served users with different mental models than the ones I had been optimizing for. When I overrode her decisions based on my own aesthetic preferences, I made the work worse, not better. More importantly, I undermined the ownership she needed to do good work over the long term.
The discipline the lead role requires is the discipline to ask "will this work for users?" rather than "would I have made this choice?" Those are different questions. The first is useful. The second produces a team of designers who are executing someone else's taste rather than developing their own judgment.