A young scientist who hopes to make discoveries is badly advised if his teacher tells him, "Go round and observe," and he is well advised if his teacher tells him: "Try to learn what people are discussing nowadays in science. Find out where difficulties arise, and take an interest in disagreements. These are the questions which you should take up."
Conjectures and Refutations: The Growth of Scientific Knowledge, Chapter 4 (p. 129), Harper & Row, Publishers. 1963