The Man Who Knew Infinity, about Ramanujan, is a biography that I reread regularly, if only as an example of somebody who continued to do what he loved against all odds. Whenever I get overly frustrated with a math or programming problem that I can't seem to overcome, I go through some of my favorite passages in there, if only to remind myself how lucky I am to be able to what I love with the support of the people in my life. Also, I can now safely say that reading The Autobiography of Malcolm X in high school was a key moment in my personal development.
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