Most of us tend to use intuition when it comes to judging: Have I found the right answer yet? This works under certain conditions, however, and not others. If you know something about the subject, then you can probably judge if you "got it." If the question is very straightforward, of course, you know. But for other searches - often the ones most important to us - it might be difficult. As Kahneman's book covers, having accurate intuition about an answer is not magic. It is a long-acquired skill obtained after many hours. A surgeon's "guess" about the root cause of an illness. A teacher's know-how in determining how to approach teaching something. A car mechanic's choice of a car part or tool that will solve the problem. You need to immerse yourself - to learn "the language" and to see the "ins-and-outs" of the situation.
The main pitfall that we are tempted into. When faced with an inherently difficult question, we often answer an easier question instead of the difficult one. And we usually do so, without noticing the substitution. Think about it.