Every small business has at least one. The person who knows which supplier to call when the usual one is out. The one who remembers why you bill that customer differently. The one whose head holds the reason behind half your process.
You do not notice it while they are there. That is the whole problem.
The issue is not the person, it is the width of the door
The risk shows up when they leave, but it is there long before. Anything only one person can do is a job that stops when that person is on holiday, out sick, or busy with something else. You feel it as a business that keeps waiting on one desk.
Owners usually read that as a people problem and try to solve it by hiring. It is not a people problem. It is a documentation and coverage problem, and hiring a second person without fixing it just gives you two undocumented roles instead of one.
Find them before they find you
This takes an hour and needs no software.
Write down the things your business does every week that a customer would notice if they stopped. Billing going out. Orders getting placed. The schedule being set. Payroll being run. Then put a name next to each one, and a second name if anyone else could genuinely do it today.
Every line with one name is a single point of failure. Most owners doing this the first time find three or four, and are surprised by at least one of them.
Close them in the cheapest order
Not all of these are worth the same effort, so do not treat them equally.
Start with the ones that are frequent and routine. A weekly task with a clear right answer is the easiest to write down and hand over, and it buys back the most time. Write the steps as you do it next time, in whatever form you will actually reread. A page in a shared folder beats a polished document nobody opens.
Then take the ones that are rare but serious. Nobody remembers the annual filing or the insurance renewal because it happens once. Those belong on a calendar with a note attached, not in someone's memory.
Leave the genuine judgment calls last. Some knowledge really is experience and will not compress into a checklist. What you can capture is the reasoning: why this customer gets different terms, what went wrong the last time you tried it the other way. That context is what a new person actually needs, and it is what nobody thinks to write down.
A note on who should hold what
Patrick Lencioni's Working Genius model is useful here, because the reason documentation never gets done is usually that it has been given to the wrong person. Writing things down is Tenacity and Enablement work. If you have handed it to the person on your team whose energy is in ideas and starting things, it will keep slipping, and they will keep feeling bad about it. Give it to whoever finishes things, and it gets finished.
The honest version
You will not close every gap, and you do not need to. The goal is that no single absence stops the business, and that if someone left tomorrow you would be replacing a role rather than reconstructing one.
If you want an outside read on where your single points of failure are, that is the kind of thing we look at first with a new client. Happy to talk it through: m7fractional.com.