In this field, almost everything is already discovered, and all that remains is to fill a few unimportant holes.

— Paraphrase of Philipp von Jolly (1809–1884), the Munich physics professor who reportedly gave this advice to a young Max Planck in 1874. The line gets attributed to Lord Kelvin online; Quote Investigator’s tracing finds the Kelvin attribution unsupported. The story is famous for being immediately wrong — Planck went on to invent quantum mechanics within thirty years.