Mark Twain said this quote

“ What a wee little part of a person's life are his acts and his words! His real life is led in his head, and is known to none but himself. All day long, the mill of his brain is grinding, and his thoughts, not those of other things, are his history. These are his life, and they are not written. Everyday would make a whole book of 80,000 words -- 365 books a year. Biographies are but the clothes and buttons of the man -- the biography of the man himself cannot be written. ”