It is the greatest of all mistakes to do nothing because you can only do little. Do what you can.

Sydney Smith (1771-1845) English clergyman, essayist, wit

Lecture (1804-1806), Moral Philosophy, No. 19 “On the Conduct of the Understanding, Part 2” Royal Institution, London
    (Source)

Collected in Elementary Sketches of Moral Philosophy (1849).