I would say the word that least describes Mark Twain (Samuel Clemens) is "secure." His life was far from secure - ever -- but especially when he was a teenager. He became a printer's apprentice when he was only 15 years old, left home at 18 and worked as a printer in New York, Philadelphia, Chicago, among other cities. He spent his evenings in public libraries and became an autodidact - that is, he taught himself. He was daring, imaginative and most likely competitive as well. He later trained himself well enough to become qualified as a river boat pilot (after his teen years), and the amount of information required for that designation was very rigorous. It took him more than two years to study everything he needed to know to become a river boat pilot, so this tells us that he was driven.
These qualities followed him into his adult life, not always with great success. He had constant financial problems due to making bad investments in some rather crazy schemes and inventions and his imagination led him to become involved in the paranormal. Even though he earned a great deal of money from his writing, he never became rich because he was overly daring in his investments.
What do YOU think?