One never notices what has been done; one can only see what remains to be done.

Marie Curie (1867-1934) Polish-French physicist and chemist [b. Maria Salomea Skłodowska]

Letter to her brother Joseph (1894-03-18)
    (Source)

As quoted in Eve Curie Labouisse, Madame Curie: A Biography, ch. 9 (1937) [tr. Sheean (1938)].