Ask HN: Generalists, when do you say "I know enough" about any particular topic?

All you need is decades old CS mostly. Then you apply this to production via software engineering principles. Systems design is the key. Always systems design. If you find something that happens to be novel then you research until the novel thing fits your mental map.

A theoretician in the purest sense is removed from practical constraints and timelines. He can, in principle, keep pursuing a subject until the day he dies.

A practitioner is aiming for a practical result within a time frame. Because he has to deliver, he cannot afford to focus on developing a deep or exhaustive grasp of any particular thing. His focus isn't knowledge, after all, but the practical result. He will lean more on what he already knows, however limited, rather than pursuing new knowledge. He is less concerned with verifying the truth of claims himself and more concerned with trusting claims tactically by knowing whom to trust and when.

So, in the capacity of practitioner, you must learn prudence, which is the virtue of knowing what should be done in a given situation. It is the basis for the moral life, as morality concerns itself with right action and right decision making.

The honest answer is that I stop caring if I lose curiosity. The rationalized answer is that expertise requires maintenance, and a low likelihood of using some expertise doesn't justify that maintenance. For example, I am unlikely to ever do advanced financial planning, and I can re-learn / lookup the formulas for doing calculations, or maybe even re-derive them if I really need to. On demand learning!

1) I get bored

2) Something with a higher priority comes up

The real Q. is “When do you stop learning?”

A. When you dangerous enough