<i>Learned Optimism</i> by Martin Seligman, while not the most influential book I've read, affects my thinking on a daily basis. Whenever something bad happens to me or I come across a mental block, I use a few techniques from the book to keep it from affecting me.<p>Keep in mind, my definition of "bad" is pretty loose. For example, one of the bad events I encounter on a regular basis is being stumped by a difficult math problem. If I were to allow myself to fall into a pessimistic line of thinking, it would make solving problems that much harder in the future.<p>Seligman found that pessimistic people learn to be helpless and that once they do, they stop believing in their ability to change things. For example, a certain subset of subjects who were given a series of unsolvable problems were unable to solve simple anagrams afterward. These people, according to the theory, learned to be helpless. However, there was a subset of people who were able to solve the anagrams. These were the people, according to the theory, who had developed the ability to remain optimistic in spite of misfortune.<p>Amazon link to the book: <a href="http://www.amazon.com/o/ASIN/1400078393/" rel="nofollow">http://www.amazon.com/o/ASIN/1400078393/</a>