It is the most difficult thing to understand, and perhaps the single biggest differentiator between a good leader and a mere manager.
The moment you start leading a team of people, your main responsibility shifts to them.
It is not to your boss, it is not to the management team, it is not to the executives, to other departments, to the board or to the company. Of course you also have responsibilities to these individuals and groups. But the main one, the one that defines your role, the one for which you will be measured in your leadership skills is to the people you lead.
Do you know them? Do you know their fears, motivators, ambitions, strengths? Do you know how they feel? Are you ready to have difficult conversations with them? Do you have an idea of where they have been professionally and have a plan for their future development? Do they come to you with ideas? Do you challenge them with problems? How do you discuss with them about their mistakes?
It is an extremely important relationship to build. And you have to allocate time for that before anything else.