"How to Win Friends & Influence People"
by Dale Carnegie
A former bacon and lard salesman for Armour & Co., Carnegie wrote this classic during the Great Depression for those in search of self-improvement.
Carnegie's big idea: By changing your actions, you change the reactions of others. Seventy-two years later his thesis holds up. After all, it doesn't matter how compelling your pitch is; if people don't like being around you, they won't buy whatever it is you're selling.