“Here Chopin has the conviction that he has lost his power of expression. With the determination to discover whether his brain can still originate ideas, he strikes his head with a hammer (here the sixteenths and thirty-seconds are to be carried out in exact time, indicating a double stroke of the hammer). In the third and fourth measures on can hear the blood trickle (trills in the left hand). He is desperate at finding no inspiration (fifth measure); he strikes again with the hammer and with greater force (thirty-second notes twice in succession during the crescendo). In the key of A flat he finds his powers again. Appeased, he seeks his former key and closes contentedly.”

Source: "The Conduct of Inquiry", p. 28.
Context: In addition to the social pressures from the scientific community there is also at work a very human trait of individual scientist. I call it the law of the instrument, and it may be formulated as follows: Give a small boy a hammer, and he will find that everything he encounters needs pounding. It comes as no particular surprise to discover that a scientist formulates problems in a way which requires for their solution just those techniques in which he himself is especially skilled.

Source: Saint Genet, Actor and Martyr (1952) (67)

Compare Poor Richard's Almanack (1758) : When you're an Anvil, hold you still, When you're a Hammer, strike your Fill.
Introductio ad prudentiam: Part II (1727), Gnomologia (1732)

Jacula Prudentum (1651)

Source: Titus Andronicus

After.
Bartlett's Familiar Quotations, 10th ed. (1919)

Interview with Einstein (1930)