After a while, Himmler realized that the "Einsatzgruppen"s methods were not the best way to kill people as quickly and cheaply as possible. He also found that many "Einsatzgruppen" had trouble killing so many people. Some had physical and mental health problems, and others became alcoholics. Himmler made a final decision after watching a mass execution in August 1941. He decided that shooting Jews was too stressful for his men.