The best leaders I know are exceedingly aware of the finiteness of their own time, energy, and attention. They know full well the import of keeping focused on a few VERY IMPORTANT objectives. These leaders avoid, with great discipline, being distracted from those uber goals.
The best of the best of those leaders are also exceedingly aware of the finiteness of the time, energy, and attention of their team. Thus, those leaders are quite deliberate in protecting their team from flavor-of-the-month initiatives and mission creep. They are just as protective of their team as they are of themselves.
It's not as much about self- or team protection as it is about staying attentive to that which is truly important, and dedicating accordingly the precious and finite tangible/intangible resources with laser-like focus.