General principles are not the less true or important because from their nature they elude immediate observation; they are like the air, which is not the less necessary because we neither see nor feel it.
Source: In The Ultimate Success Quotations Library, 1997.
-- William Hazlitt, (Apr 10 1778-1830), English writer, essayist; He wrote Characters of Shakespeare's Plays, 1817; also noted for essays on value of humanity.