Ben Kuhn, Categories of leadership on technical teams:
More importantly, though, we often want to somehow split these responsibilities between people. Team leadership covers a huge array of things—as you can see from how long this post is—and trying to find someone who can be great at all of them is often a unicorn hunt. Even if you do find someone good-enough at all of them, they usually spike in 1-2 areas, and it might be higher-leverage for them to fully focus on those.
If you find yourself in a wholly new team, this might help you find your way to traction. If you find yourself confused by the (rapidly) changing nature of work and need to zoom out on the team/role you find yourself leading, this will help!
Even if you’ve been in your job/team/organization for a while, to paraphrase David Byrne, “You may tell yourself, this is not the job I signed up for! / My god, have I have I done?”, in which case this mental model is also helpful. (And, good luck!)