In earlier military conflicts relatively few U.S. military personnel succumbed to addiction. What distinguished the Vietnam experience from these wars? The ready availability of pure heroin and of other drugs is only part of the answer. This war, unlike previous ones, quickly lost meaning for those ordered to fight and die in the faraway jungles and fields of Southeast Asia. There was too wide a gap between what they’d been told and the reality they witnessed and experienced. Lack of meaning, not simply the dangers and privations of war, was the major source of the stress that triggered their flight to oblivion.

— hungry-ghostsch. 12