"We must know, we shall know." -- David Hilbert
David Hilbert was a great German mathematician. What I appreciate the most about him is his quixotic personality and single-mindedness, going along with Bertrand Russel on their impossible quest to clean mathematics of all doubt and uncertainty, always searching for strict solutions through pure thought. In 1900, Hilbert came up with a list of 23 fundamental problems, many of which are still being investigated to this day. In 1930, Hilbert finished a famous speech in Königsberg with the words "We must know, we shall know", a phrase that fits perfectly the life-long devotion he had for mathematics.