Success in the stock market comes naturally if one lets it be. Investing in stocks is a significant building block for retirement security. Analyses of several portfolios from private investors have shown that investors often make avoidable mistakes. In addition to insufficient diversification and incorrect sector and country allocation, it is particularly human weaknesses that cost good money in the stock market and cause many investors sleepless nights. Here, the main mistakes are presented unflinchingly, and solutions to the dilemma are highlighted. Well-founded, yet always easy to understand and sprinkled with a touch of humor.