In his laboratory at St Mary's, Paddington, London (1943)

Alexander Fleming
(*6. August 1881 Darvel, East Ayrshire, Schottland - †11. März 1955 London)

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"I have been trying to point out that in our lives chance may have an astonishing influence and, if I may offer advice to the young laboratory worker, it would be this—never neglect an extraordinary appearance or happening. It may be—usually is, in fact—a false alarm that leads to nothing, but may on the other hand be the clue provided by fate to lead you to some important advance."

Lecture at Harvard University. Quoted in Joseph Sambrook, David W. Russell, Molecular Cloning (2001), Vol. 1, 153.