What is the thing in your business that only works because you personally show up for it?

Every business I run has at least one process that has never actually been written down, it lives in my head, and it works only because I am the one doing it every time. I did not plan it that way, it just accumulated, a client relationship only I manage, a schedule only I remember the exceptions to, a quality check only I know how to do properly.

The question I keep avoiding is what happens the week I am unreachable. Curious whether you have identified yours, and whether you have actually done anything about it, or just quietly hoped you never have to find out.