Minsky labelled our minds "difference engines". This means, we work best with a goal. The moment some sort of goal is set, the mind keeps diffing goal and your current position continuously. Given this framework, I always tend to have a higher goal, some result I hope to see. With such context, then it is simply a matter of asking "is it working now? am I there yet?". If it is not, learn more. If it is, then I sort of know enough. And if I have a stronger urge, I may go on a curiosity-ride for as long as (economically) possible :)