There is a specific moment, familiar to anyone who has learned anything properly, when a subject stops being simple.
You arrive knowing nothing, and the field looks small. You read for a month and it looks enormous. You read for a year and it looks enormous in a different way: you can now see the shape of the parts you have not read, and you have acquired the ability to be embarrassed by what you said in month one.
That second expansion is the useful one. It is also the point at which many people quietly stop, because the feeling it produces is indistinguishable from getting worse.
Two kinds of not knowing
It is worth separating them, because they behave very differently.
The first is ignorance you can see. You know that you do not know how the tax system treats a particular kind of income; you know where the answer would be found; you can price the cost of finding out. This kind is almost harmless. It is a task.
The second is ignorance you cannot see — the question you did not know was a question. This is the expensive kind, and no amount of confidence protects against it. In fact confidence is the mechanism by which it does its damage, because a person who feels informed does not go looking.
Breadth is the only reasonable defence. Not because a general education makes you right, but because a person who has been a beginner in eight fields has a working sense of how much a field contains, and is therefore much harder to convince that any of them are simple.
Saying it out loud
The practical part of this principle is social rather than intellectual. Almost everyone privately knows the limits of their expertise. Far fewer will state them in a meeting.
This is a shame, because the phrase I don’t know, but I know how we could find out is one of the most productive sentences available in any professional setting. It ends a category of unwinnable argument, it converts posturing into a task, and — reliably, in our experience — it gives everyone else in the room permission to admit the same thing.
Expertise is not the absence of ignorance. It is an unusually accurate map of where your ignorance begins.