In a lot of small businesses, the knowledge of how things actually get done exists in exactly one place: the owner's head. How a particular customer likes to be handled, the steps to close the month's books, the quirk in the supplier's ordering system, the reason things are done this way and not that - all of it lives as memory and habit, never written down because it never needed to be. While the owner is present and doing everything, this works seamlessly. It becomes a problem the moment the business needs to run without the owner doing every part of it personally, which is to say the moment the business tries to grow, delegate, or simply give the owner a break.
The costs of keeping everything undocumented show up at precisely the transitions a business most wants to make. You cannot delegate a task effectively if the only version of how to do it is in your head and you must explain it from scratch each time - so you end up doing it yourself, which caps the business at your personal capacity. You cannot take a genuine holiday or absorb an illness if operations stop the moment you are unavailable, because nobody else knows how the essential things are done. Training a new hire becomes slow and error-prone, since there is nothing to hand them but your intermittent attention. And should you ever want to sell the business, a buyer is purchasing something alarming: an operation whose knowledge walks out the door with the seller, which is worth far less than one that can run on its own.
There is a quieter cost too, which is fragility. A business that depends on one person's undocumented knowledge is one bad event away from serious trouble - if that person is suddenly unavailable, the operation does not just lose a worker, it loses the instructions for its own functioning. Even in the ordinary course, undocumented processes drift and degrade: they are done slightly differently each time, mistakes recur because the lessons were never captured, and improvements are lost when the person who knew the better way forgets or leaves. What feels like efficient informality is often accumulated risk and quiet waste, invisible only because the person holding it all together has not yet been removed from the equation.
The remedy does not require a bureaucracy, only the habit of writing down how the important things are done as you do them. Not everything needs documenting - the aim is the core, repeatable processes that the business depends on and that someone else might one day need to perform: the steps, the reasons, the things that go wrong and how to handle them. Done incrementally, a little at a time, this turns private habit into a shared asset the business owns rather than rents from the owner's memory. It is what makes delegation possible, what lets the business survive the owner's absence, and what turns a job that happens to have a name into a business that could genuinely run, grow, or be sold without its founder holding every thread. A business that only works because it is all in your head is, in an important sense, not yet a business at all.