It seems that life is not easy for any of us. But what of that? We must have perseverance and above all confidence in ourselves. We must believe that we are gifted for something, and that this thing, at whatever cost, must be attained.

[La vie n’est facile pour aucun de nous. Mais quoi, il faut avoir de la persévérance, et surtout de la confiance en soi. Il faut croire que l’on est doué pour quelque chose, et que, cette chose, il faut l’atteindre coûte que coûte.]

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

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

(French (Source))

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