A team captaincy is the first job where the outcome depends on people under no obligation to do what you say. Most of leadership is that job.
You have no authority. You cannot fire anyone, you do not set their compensation, and several of them are better than you at the actual task.
Whatever influence exists has to be earned continuously and can be withdrawn without notice.
Formal authority works in a narrow band. It compels compliance, and compliance is enough for tasks and nothing else.
Everything that requires discretionary effort — the extra hour, the thing nobody asked for, the honest objection — is voluntary regardless of the reporting line.
Authority gets you compliance. Everything valuable is discretionary.
Doing the unpleasant work visibly. Being consistent, so people can predict you. Being right often enough to be worth listening to, and being clear when you are not.
And taking the blame publicly and giving credit publicly, which is the cheapest and most under-used mechanism available.
Trying to be liked. A captain optimising for popularity avoids the conversation that needs having, and the team notices immediately.
Respect and affection are different, and only one of them survives a hard season.
Nearly everywhere. Co-founders, partners, boards, vendors, and anyone senior enough to have options. None of them can be managed by authority.
It does not scale by effort. You cannot earn influence with fifty people the way you earn it with eleven, which is why founders who were excellent at ten struggle at fifty.
At that point it has to come through other people, and that is a different job again.